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 $104.92   13.117%   $118.6824   $118.68   $118.70   $118.70  
  Purchase #2 $219.44   12.236%   $246.2907   $246.29   $246.30   $246.30  
  Purchase #3 $228.29   5.389%   $240.5925   $240.59   $240.60   $240.60  
  Purchase #4 $224.57   8.180%   $242.9398   $242.94   $242.95   $242.90  
  Purchase #5 $126.26   4.553%   $132.0086   $132.01   $132.00   $132.00  
  Purchase #6 $83.75   5.819%   $88.6234   $88.62   $88.60   $88.60  
  Purchase #7 $112.82   11.533%   $125.8315   $125.83   $125.85   $125.80  
  7 purchase totals = $1,100.05       $1,194.9689   $1,194.96   $1,195.00   $1,194.90