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 $208.49   13.157%   $235.921   $235.92   $235.90   $235.90  
  Purchase #2 $40.96   9.517%   $44.8582   $44.86   $44.85   $44.90  
  Purchase #3 $37.54   9.403%   $41.0699   $41.07   $41.05   $41.10  
  Purchase #4 $62.39   7.728%   $67.2115   $67.21   $67.20   $67.20  
  Purchase #5 $41.60   11.285%   $46.2946   $46.29   $46.30   $46.30  
  Purchase #6 $147.91   11.788%   $165.3456   $165.35   $165.35   $165.30  
  Purchase #7 $178.48   13.679%   $202.8943   $202.89   $202.90   $202.90  
  7 purchase totals = $717.37       $803.5951   $803.59   $803.55   $803.60