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 $59.98   11.167%   $66.678   $66.68   $66.70   $66.70  
  Purchase #2 $193.96   7.178%   $207.8824   $207.88   $207.90   $207.90  
  Purchase #3 $84.28   8.197%   $91.1884   $91.19   $91.20   $91.20  
  Purchase #4 $229.75   9.555%   $251.7026   $251.70   $251.70   $251.70  
  Purchase #5 $141.43   8.795%   $153.8688   $153.87   $153.85   $153.90  
  Purchase #6 $173.48   12.445%   $195.0696   $195.07   $195.05   $195.10  
  Purchase #7 $82.86   7.148%   $88.7828   $88.78   $88.80   $88.80  
  7 purchase totals = $965.74       $1,055.1726   $1,055.17   $1,055.20   $1,055.30