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 $247.73   8.354%   $268.4254   $268.43   $268.45   $268.40  
  Purchase #2 $134.59   11.290%   $149.7852   $149.79   $149.80   $149.80  
  Purchase #3 $78.68   6.413%   $83.7257   $83.73   $83.75   $83.70  
  Purchase #4 $111.60   12.790%   $125.8736   $125.87   $125.85   $125.90  
  Purchase #5 $11.95   13.823%   $13.6018   $13.60   $13.60   $13.60  
  Purchase #6 $206.32   3.814%   $214.189   $214.19   $214.20   $214.20  
  Purchase #7 $164.44   3.754%   $170.6131   $170.61   $170.60   $170.60  
  7 purchase totals = $955.31       $1,026.2138   $1,026.22   $1,026.25   $1,026.20