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 $112.76   11.348%   $125.556   $125.56   $125.55   $125.60  
  Purchase #2 $12.75   6.108%   $13.5288   $13.53   $13.55   $13.50  
  Purchase #3 $29.69   11.491%   $33.1017   $33.10   $33.10   $33.10  
  Purchase #4 $20.39   11.350%   $22.7043   $22.70   $22.70   $22.70  
  Purchase #5 $27.85   13.776%   $31.6866   $31.69   $31.70   $31.70  
  Purchase #6 $241.73   11.445%   $269.396   $269.40   $269.40   $269.40  
  Purchase #7 $202.59   12.548%   $228.011   $228.01   $228.00   $228.00  
  7 purchase totals = $647.76       $723.9844   $723.99   $724.00   $724.00