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 $191.59   6.127%   $203.3287   $203.33   $203.35   $203.30  
  Purchase #2 $126.30   6.252%   $134.1963   $134.20   $134.20   $134.20  
  Purchase #3 $17.98   5.154%   $18.9067   $18.91   $18.90   $18.90  
  Purchase #4 $50.39   7.702%   $54.271   $54.27   $54.25   $54.30  
  Purchase #5 $42.50   8.621%   $46.1639   $46.16   $46.15   $46.20  
  Purchase #6 $236.30   13.604%   $268.4463   $268.45   $268.45   $268.40  
  Purchase #7 $167.56   5.746%   $177.188   $177.19   $177.20   $177.20  
  7 purchase totals = $832.62       $902.5009   $902.51   $902.50   $902.50