Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.84   10.352%   $272.3929   $272.39   $272.40   $272.40  
  Purchase #2 $112.74   5.647%   $119.1064   $119.11   $119.10   $119.10  
  Purchase #3 $187.43   7.107%   $200.7507   $200.75   $200.75   $200.80  
  Purchase #4 $115.66   3.322%   $119.5022   $119.50   $119.50   $119.50  
  Purchase #5 $242.96   7.560%   $261.3278   $261.33   $261.35   $261.30  
  Purchase #6 $230.74   6.853%   $246.5526   $246.55   $246.55   $246.60  
  Purchase #7 $217.31   11.543%   $242.3941   $242.39   $242.40   $242.40  
  7 purchase totals = $1,353.68       $1,462.0267   $1,462.02   $1,462.05   $1,462.10