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 $55.33   11.232%   $61.5447   $61.54   $61.55   $61.50  
  Purchase #2 $177.63   7.804%   $191.4922   $191.49   $191.50   $191.50  
  Purchase #3 $240.84   12.489%   $270.9185   $270.92   $270.90   $270.90  
  Purchase #4 $168.87   4.170%   $175.9119   $175.91   $175.90   $175.90  
  Purchase #5 $178.74   11.578%   $199.4345   $199.43   $199.45   $199.40  
  Purchase #6 $111.98   8.397%   $121.383   $121.38   $121.40   $121.40  
  Purchase #7 $215.72   12.190%   $242.0163   $242.02   $242.00   $242.00  
  7 purchase totals = $1,149.11       $1,262.7011   $1,262.69   $1,262.70   $1,262.60