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 $53.29   12.795%   $60.1085   $60.11   $60.10   $60.10  
  Purchase #2 $76.28   13.332%   $86.4496   $86.45   $86.45   $86.40  
  Purchase #3 $15.98   12.609%   $17.9949   $17.99   $18.00   $18.00  
  Purchase #4 $92.85   10.565%   $102.6596   $102.66   $102.65   $102.70  
  Purchase #5 $60.37   12.597%   $67.9748   $67.97   $67.95   $68.00  
  Purchase #6 $201.62   8.378%   $218.5117   $218.51   $218.50   $218.50  
  Purchase #7 $187.67   3.649%   $194.5181   $194.52   $194.50   $194.50  
  7 purchase totals = $688.06       $748.2172   $748.21   $748.15   $748.20