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 $65.89   11.244%   $73.2987   $73.30   $73.30   $73.30  
  Purchase #2 $60.93   3.409%   $63.0071   $63.01   $63.00   $63.00  
  Purchase #3 $12.34   9.656%   $13.5316   $13.53   $13.55   $13.50  
  Purchase #4 $212.73   7.382%   $228.4337   $228.43   $228.45   $228.40  
  Purchase #5 $197.76   3.367%   $204.4186   $204.42   $204.40   $204.40  
  Purchase #6 $168.27   5.597%   $177.6881   $177.69   $177.70   $177.70  
  Purchase #7 $160.59   7.838%   $173.177   $173.18   $173.20   $173.20  
  7 purchase totals = $878.51       $933.5548   $933.56   $933.60   $933.50