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 $67.42   10.590%   $74.5598   $74.56   $74.55   $74.60  
  Purchase #2 $247.67   4.839%   $259.6548   $259.65   $259.65   $259.70  
  Purchase #3 $7.30   12.223%   $8.1923   $8.19   $8.20   $8.20  
  Purchase #4 $87.91   5.310%   $92.578   $92.58   $92.60   $92.60  
  Purchase #5 $155.71   13.340%   $176.4817   $176.48   $176.50   $176.50  
  Purchase #6 $234.93   7.242%   $251.9436   $251.94   $251.95   $251.90  
  Purchase #7 $78.42   13.623%   $89.1032   $89.10   $89.10   $89.10  
  7 purchase totals = $879.36       $952.5134   $952.50   $952.55   $952.60