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 $84.94   12.691%   $95.7197   $95.72   $95.70   $95.70  
  Purchase #2 $129.55   9.250%   $141.5334   $141.53   $141.55   $141.50  
  Purchase #3 $46.45   11.735%   $51.9009   $51.90   $51.90   $51.90  
  Purchase #4 $244.98   4.795%   $256.7268   $256.73   $256.75   $256.70  
  Purchase #5 $33.96   4.481%   $35.4817   $35.48   $35.50   $35.50  
  Purchase #6 $130.71   3.181%   $134.8679   $134.87   $134.85   $134.90  
  Purchase #7 $99.63   10.586%   $110.1768   $110.18   $110.20   $110.20  
  7 purchase totals = $770.22       $826.4072   $826.41   $826.45   $826.40