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 $237.81   10.440%   $262.6374   $262.64   $262.65   $262.60  
  Purchase #2 $197.91   9.621%   $216.9509   $216.95   $216.95   $217.00  
  Purchase #3 $247.42   7.447%   $265.8454   $265.85   $265.85   $265.80  
  Purchase #4 $55.48   11.457%   $61.8363   $61.84   $61.85   $61.80  
  Purchase #5 $241.73   8.291%   $261.7718   $261.77   $261.75   $261.80  
  Purchase #6 $95.52   6.340%   $101.576   $101.58   $101.60   $101.60  
  Purchase #7 $47.32   11.214%   $52.6265   $52.63   $52.65   $52.60  
  7 purchase totals = $1,123.19       $1,223.2443   $1,223.26   $1,223.30   $1,223.20