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 $52.52   11.437%   $58.5267   $58.53   $58.55   $58.50  
  Purchase #2 $141.87   4.801%   $148.6812   $148.68   $148.70   $148.70  
  Purchase #3 $150.25   11.117%   $166.9533   $166.95   $166.95   $167.00  
  Purchase #4 $208.25   12.625%   $234.5416   $234.54   $234.55   $234.50  
  Purchase #5 $31.64   9.231%   $34.5607   $34.56   $34.55   $34.60  
  Purchase #6 $60.55   12.191%   $67.9317   $67.93   $67.95   $67.90  
  Purchase #7 $173.64   11.788%   $194.1087   $194.11   $194.10   $194.10  
  7 purchase totals = $818.72       $905.3039   $905.30   $905.35   $905.30