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 $232.79   12.465%   $261.8073   $261.81   $261.80   $261.80  
  Purchase #2 $179.54   10.817%   $198.9608   $198.96   $198.95   $199.00  
  Purchase #3 $64.33   13.749%   $73.1747   $73.17   $73.15   $73.20  
  Purchase #4 $98.86   11.739%   $110.4652   $110.47   $110.45   $110.50  
  Purchase #5 $45.42   5.390%   $47.8681   $47.87   $47.85   $47.90  
  Purchase #6 $135.33   8.863%   $147.3243   $147.32   $147.30   $147.30  
  Purchase #7 $169.68   8.769%   $184.5592   $184.56   $184.55   $184.60  
  7 purchase totals = $925.95       $1,024.1596   $1,024.16   $1,024.05   $1,024.30