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 $211.61   6.441%   $225.2398   $225.24   $225.25   $225.20  
  Purchase #2 $159.51   8.584%   $173.2023   $173.20   $173.20   $173.20  
  Purchase #3 $104.69   3.724%   $108.5887   $108.59   $108.60   $108.60  
  Purchase #4 $81.27   6.767%   $86.7695   $86.77   $86.75   $86.80  
  Purchase #5 $49.61   3.540%   $51.3662   $51.37   $51.35   $51.40  
  Purchase #6 $18.62   8.206%   $20.148   $20.15   $20.15   $20.10  
  Purchase #7 $249.97   13.736%   $284.3059   $284.31   $284.30   $284.30  
  7 purchase totals = $875.28       $949.6204   $949.63   $949.60   $949.60