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 $244.47   8.706%   $265.7536   $265.75   $265.75   $265.80  
  Purchase #2 $120.96   11.449%   $134.8087   $134.81   $134.80   $134.80  
  Purchase #3 $144.51   12.348%   $162.3541   $162.35   $162.35   $162.40  
  Purchase #4 $159.62   7.811%   $172.0879   $172.09   $172.10   $172.10  
  Purchase #5 $211.54   11.559%   $235.9919   $235.99   $236.00   $236.00  
  Purchase #6 $138.73   9.207%   $151.5029   $151.50   $151.50   $151.50  
  Purchase #7 $113.32   10.567%   $125.2945   $125.29   $125.30   $125.30  
  7 purchase totals = $1,133.15       $1,247.7936   $1,247.78   $1,247.80   $1,247.90