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 $233.58   5.327%   $246.0228   $246.02   $246.00   $246.00  
  Purchase #2 $220.32   5.424%   $232.2702   $232.27   $232.25   $232.30  
  Purchase #3 $78.26   7.198%   $83.8932   $83.89   $83.90   $83.90  
  Purchase #4 $138.73   4.575%   $145.0769   $145.08   $145.10   $145.10  
  Purchase #5 $147.45   11.675%   $164.6648   $164.66   $164.65   $164.70  
  Purchase #6 $35.70   13.807%   $40.6291   $40.63   $40.65   $40.60  
  Purchase #7 $131.25   8.607%   $142.5467   $142.55   $142.55   $142.50  
  7 purchase totals = $985.29       $1,055.1037   $1,055.10   $1,055.10   $1,055.10