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 $224.31   9.234%   $245.0228   $245.02   $245.00   $245.00  
  Purchase #2 $118.75   5.757%   $125.5864   $125.59   $125.60   $125.60  
  Purchase #3 $204.47   6.434%   $217.6256   $217.63   $217.65   $217.60  
  Purchase #4 $172.99   9.654%   $189.6905   $189.69   $189.70   $189.70  
  Purchase #5 $143.72   12.324%   $161.4321   $161.43   $161.45   $161.40  
  Purchase #6 $110.45   6.408%   $117.5276   $117.53   $117.55   $117.50  
  Purchase #7 $220.76   8.160%   $238.774   $238.77   $238.75   $238.80  
  7 purchase totals = $1,195.45       $1,295.6590   $1,295.66   $1,295.70   $1,295.60