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 $58.26   8.478%   $63.1993   $63.20   $63.20   $63.20  
  Purchase #2 $96.55   3.165%   $99.6058   $99.61   $99.60   $99.60  
  Purchase #3 $156.56   11.285%   $174.2278   $174.23   $174.25   $174.20  
  Purchase #4 $182.29   7.305%   $195.6063   $195.61   $195.60   $195.60  
  Purchase #5 $129.27   5.213%   $136.0088   $136.01   $136.00   $136.00  
  Purchase #6 $236.94   8.141%   $256.2293   $256.23   $256.25   $256.20  
  Purchase #7 $229.43   10.649%   $253.862   $253.86   $253.85   $253.90  
  7 purchase totals = $1,089.30       $1,178.7393   $1,178.75   $1,178.75   $1,178.70