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 $67.56   11.816%   $75.5429   $75.54   $75.55   $75.50  
  Purchase #2 $76.37   11.559%   $85.1976   $85.20   $85.20   $85.20  
  Purchase #3 $150.83   9.533%   $165.2086   $165.21   $165.20   $165.20  
  Purchase #4 $128.84   3.397%   $133.2167   $133.22   $133.20   $133.20  
  Purchase #5 $206.30   13.605%   $234.3671   $234.37   $234.35   $234.40  
  Purchase #6 $92.97   8.439%   $100.8157   $100.82   $100.80   $100.80  
  Purchase #7 $92.84   10.486%   $102.5752   $102.58   $102.60   $102.60  
  7 purchase totals = $815.71       $896.9238   $896.94   $896.90   $896.90