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 $231.79   9.799%   $254.5031   $254.50   $254.50   $254.50  
  Purchase #2 $9.82   7.498%   $10.5563   $10.56   $10.55   $10.60  
  Purchase #3 $73.47   3.804%   $76.2648   $76.26   $76.25   $76.30  
  Purchase #4 $139.81   3.477%   $144.6712   $144.67   $144.65   $144.70  
  Purchase #5 $200.82   5.124%   $211.11   $211.11   $211.10   $211.10  
  Purchase #6 $210.43   9.647%   $230.7302   $230.73   $230.75   $230.70  
  Purchase #7 $181.62   5.718%   $192.005   $192.01   $192.00   $192.00  
  7 purchase totals = $1,047.76       $1,119.8406   $1,119.84   $1,119.80   $1,119.90