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 $186.79   6.872%   $199.6262   $199.63   $199.65   $199.60  
  Purchase #2 $215.81   9.323%   $235.93   $235.93   $235.95   $235.90  
  Purchase #3 $79.47   5.387%   $83.751   $83.75   $83.75   $83.80  
  Purchase #4 $221.63   10.501%   $244.9034   $244.90   $244.90   $244.90  
  Purchase #5 $227.78   11.694%   $254.4166   $254.42   $254.40   $254.40  
  Purchase #6 $119.93   9.378%   $131.177   $131.18   $131.20   $131.20  
  Purchase #7 $147.83   7.639%   $159.1227   $159.12   $159.10   $159.10  
  7 purchase totals = $1,199.24       $1,308.9269   $1,308.93   $1,308.95   $1,308.90