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 $178.60   13.108%   $202.0109   $202.01   $202.00   $202.00  
  Purchase #2 $37.53   10.163%   $41.3442   $41.34   $41.35   $41.30  
  Purchase #3 $214.95   9.519%   $235.4111   $235.41   $235.40   $235.40  
  Purchase #4 $97.91   4.426%   $102.2435   $102.24   $102.25   $102.20  
  Purchase #5 $215.51   12.652%   $242.7763   $242.78   $242.80   $242.80  
  Purchase #6 $226.49   10.471%   $250.2058   $250.21   $250.20   $250.20  
  Purchase #7 $226.35   13.274%   $256.3957   $256.40   $256.40   $256.40  
  7 purchase totals = $1,197.34       $1,330.3875   $1,330.39   $1,330.40   $1,330.30