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 $67.77   12.341%   $76.1335   $76.13   $76.15   $76.10  
  Purchase #2 $22.70   7.256%   $24.3471   $24.35   $24.35   $24.30  
  Purchase #3 $61.31   7.445%   $65.8745   $65.87   $65.85   $65.90  
  Purchase #4 $170.53   8.533%   $185.0813   $185.08   $185.10   $185.10  
  Purchase #5 $141.75   9.872%   $155.7436   $155.74   $155.75   $155.70  
  Purchase #6 $124.63   6.216%   $132.377   $132.38   $132.40   $132.40  
  Purchase #7 $169.58   3.414%   $175.3695   $175.37   $175.35   $175.40  
  7 purchase totals = $758.27       $814.9265   $814.92   $814.95   $814.90