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 $55.85   12.211%   $62.6698   $62.67   $62.65   $62.70  
  Purchase #2 $192.76   8.663%   $209.4588   $209.46   $209.45   $209.50  
  Purchase #3 $232.83   5.736%   $246.1851   $246.19   $246.20   $246.20  
  Purchase #4 $69.56   5.320%   $73.2606   $73.26   $73.25   $73.30  
  Purchase #5 $144.73   11.255%   $161.0194   $161.02   $161.00   $161.00  
  Purchase #6 $172.33   5.844%   $182.401   $182.40   $182.40   $182.40  
  Purchase #7 $10.64   5.559%   $11.2315   $11.23   $11.25   $11.20  
  7 purchase totals = $878.70       $946.2262   $946.23   $946.20   $946.30