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 $70.38   12.262%   $79.01   $79.01   $79.00   $79.00  
  Purchase #2 $48.96   10.802%   $54.2487   $54.25   $54.25   $54.20  
  Purchase #3 $84.59   8.671%   $91.9248   $91.92   $91.90   $91.90  
  Purchase #4 $50.97   13.713%   $57.9595   $57.96   $57.95   $58.00  
  Purchase #5 $73.63   3.167%   $75.9619   $75.96   $75.95   $76.00  
  Purchase #6 $87.84   9.556%   $96.234   $96.23   $96.25   $96.20  
  Purchase #7 $247.91   11.426%   $276.2362   $276.24   $276.25   $276.20  
  7 purchase totals = $664.28       $731.5751   $731.57   $731.55   $731.50