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 $67.33   12.867%   $75.9934   $75.99   $76.00   $76.00  
  Purchase #2 $219.83   7.661%   $236.6712   $236.67   $236.65   $236.70  
  Purchase #3 $132.73   4.171%   $138.2662   $138.27   $138.25   $138.30  
  Purchase #4 $98.72   3.862%   $102.5326   $102.53   $102.55   $102.50  
  Purchase #5 $68.92   6.429%   $73.3509   $73.35   $73.35   $73.40  
  Purchase #6 $27.32   9.269%   $29.8523   $29.85   $29.85   $29.90  
  Purchase #7 $11.63   12.363%   $13.0678   $13.07   $13.05   $13.10  
  7 purchase totals = $626.48       $669.7344   $669.73   $669.70   $669.90