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 $233.71   11.683%   $261.0143   $261.01   $261.00   $261.00  
  Purchase #2 $181.51   8.676%   $197.2578   $197.26   $197.25   $197.30  
  Purchase #3 $118.58   12.522%   $133.4286   $133.43   $133.45   $133.40  
  Purchase #4 $84.56   10.364%   $93.3238   $93.32   $93.30   $93.30  
  Purchase #5 $250.93   7.727%   $270.3194   $270.32   $270.30   $270.30  
  Purchase #6 $140.52   8.721%   $152.7747   $152.77   $152.75   $152.80  
  Purchase #7 $202.71   6.622%   $216.1335   $216.13   $216.15   $216.10  
  7 purchase totals = $1,212.52       $1,324.2521   $1,324.24   $1,324.20   $1,324.20