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 $205.84   10.654%   $227.7702   $227.77   $227.75   $227.80  
  Purchase #2 $156.89   4.181%   $163.4496   $163.45   $163.45   $163.40  
  Purchase #3 $162.86   3.697%   $168.8809   $168.88   $168.90   $168.90  
  Purchase #4 $215.35   12.604%   $242.4927   $242.49   $242.50   $242.50  
  Purchase #5 $35.75   4.588%   $37.3902   $37.39   $37.40   $37.40  
  Purchase #6 $72.63   8.836%   $79.0476   $79.05   $79.05   $79.00  
  Purchase #7 $27.96   11.848%   $31.2727   $31.27   $31.25   $31.30  
  7 purchase totals = $877.28       $950.3039   $950.30   $950.30   $950.30