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 $42.71   4.500%   $44.632   $44.63   $44.65   $44.60  
  Purchase #2 $230.34   10.858%   $255.3503   $255.35   $255.35   $255.40  
  Purchase #3 $23.52   6.624%   $25.078   $25.08   $25.10   $25.10  
  Purchase #4 $76.29   13.663%   $86.7135   $86.71   $86.70   $86.70  
  Purchase #5 $48.69   13.276%   $55.1541   $55.15   $55.15   $55.20  
  Purchase #6 $119.60   11.214%   $133.0119   $133.01   $133.00   $133.00  
  Purchase #7 $232.90   12.140%   $261.1741   $261.17   $261.15   $261.20  
  7 purchase totals = $774.05       $861.1139   $861.10   $861.10   $861.20