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 $36.93   12.165%   $41.4225   $41.42   $41.40   $41.40  
  Purchase #2 $156.89   9.511%   $171.8118   $171.81   $171.80   $171.80  
  Purchase #3 $72.53   8.582%   $78.7545   $78.75   $78.75   $78.80  
  Purchase #4 $14.49   6.804%   $15.4759   $15.48   $15.50   $15.50  
  Purchase #5 $31.25   9.181%   $34.1191   $34.12   $34.10   $34.10  
  Purchase #6 $212.53   10.595%   $235.0476   $235.05   $235.05   $235.00  
  Purchase #7 $191.43   12.112%   $214.616   $214.62   $214.60   $214.60  
  7 purchase totals = $716.05       $791.2474   $791.25   $791.20   $791.20