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 $204.97   3.627%   $212.4043   $212.40   $212.40   $212.40  
  Purchase #2 $170.41   8.521%   $184.9306   $184.93   $184.95   $184.90  
  Purchase #3 $223.53   11.484%   $249.2002   $249.20   $249.20   $249.20  
  Purchase #4 $32.82   6.185%   $34.8499   $34.85   $34.85   $34.80  
  Purchase #5 $203.42   9.752%   $223.2575   $223.26   $223.25   $223.30  
  Purchase #6 $199.78   12.304%   $224.3609   $224.36   $224.35   $224.40  
  Purchase #7 $59.53   5.288%   $62.6779   $62.68   $62.70   $62.70  
  7 purchase totals = $1,094.46       $1,191.6813   $1,191.68   $1,191.70   $1,191.70