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 $236.98   12.722%   $267.1286   $267.13   $267.15   $267.10  
  Purchase #2 $125.31   5.848%   $132.6381   $132.64   $132.65   $132.60  
  Purchase #3 $10.46   8.479%   $11.3469   $11.35   $11.35   $11.30  
  Purchase #4 $51.42   5.568%   $54.2831   $54.28   $54.30   $54.30  
  Purchase #5 $20.96   4.540%   $21.9116   $21.91   $21.90   $21.90  
  Purchase #6 $183.88   13.530%   $208.759   $208.76   $208.75   $208.80  
  Purchase #7 $207.92   6.854%   $222.1708   $222.17   $222.15   $222.20  
  7 purchase totals = $836.93       $918.2381   $918.24   $918.25   $918.20