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 $224.42   9.821%   $246.4603   $246.46   $246.45   $246.50  
  Purchase #2 $73.63   7.706%   $79.3039   $79.30   $79.30   $79.30  
  Purchase #3 $60.38   7.688%   $65.022   $65.02   $65.00   $65.00  
  Purchase #4 $148.68   8.183%   $160.8465   $160.85   $160.85   $160.80  
  Purchase #5 $177.57   8.199%   $192.129   $192.13   $192.15   $192.10  
  Purchase #6 $69.75   7.805%   $75.194   $75.19   $75.20   $75.20  
  Purchase #7 $94.96   8.539%   $103.0686   $103.07   $103.05   $103.10  
  7 purchase totals = $849.39       $922.0243   $922.02   $922.00   $922.00