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 $119.42   6.148%   $126.7619   $126.76   $126.75   $126.80  
  Purchase #2 $41.82   8.462%   $45.3588   $45.36   $45.35   $45.40  
  Purchase #3 $57.91   7.140%   $62.0448   $62.04   $62.05   $62.00  
  Purchase #4 $50.60   5.712%   $53.4903   $53.49   $53.50   $53.50  
  Purchase #5 $189.91   9.321%   $207.6115   $207.61   $207.60   $207.60  
  Purchase #6 $30.84   12.497%   $34.6941   $34.69   $34.70   $34.70  
  Purchase #7 $170.61   13.767%   $194.0979   $194.10   $194.10   $194.10  
  7 purchase totals = $661.11       $724.0593   $724.05   $724.05   $724.10