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 $50.94   5.523%   $53.7534   $53.75   $53.75   $53.80  
  Purchase #2 $114.54   9.562%   $125.4923   $125.49   $125.50   $125.50  
  Purchase #3 $155.70   4.235%   $162.2939   $162.29   $162.30   $162.30  
  Purchase #4 $117.68   11.801%   $131.5674   $131.57   $131.55   $131.60  
  Purchase #5 $193.33   6.239%   $205.3919   $205.39   $205.40   $205.40  
  Purchase #6 $146.28   11.775%   $163.5045   $163.50   $163.50   $163.50  
  Purchase #7 $96.36   8.262%   $104.3213   $104.32   $104.30   $104.30  
  7 purchase totals = $874.83       $946.3247   $946.31   $946.30   $946.40