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 $71.62   4.714%   $74.9962   $75.00   $75.00   $75.00  
  Purchase #2 $69.29   3.299%   $71.5759   $71.58   $71.60   $71.60  
  Purchase #3 $230.96   3.475%   $238.9859   $238.99   $239.00   $239.00  
  Purchase #4 $171.59   9.804%   $188.4127   $188.41   $188.40   $188.40  
  Purchase #5 $183.49   9.660%   $201.2151   $201.22   $201.20   $201.20  
  Purchase #6 $106.31   5.241%   $111.8817   $111.88   $111.90   $111.90  
  Purchase #7 $73.54   6.806%   $78.5451   $78.55   $78.55   $78.50  
  7 purchase totals = $906.80       $965.6126   $965.63   $965.65   $965.60