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 $235.26   11.253%   $261.7338   $261.73   $261.75   $261.70  
  Purchase #2 $153.52   7.428%   $164.9235   $164.92   $164.90   $164.90  
  Purchase #3 $23.90   6.523%   $25.459   $25.46   $25.45   $25.50  
  Purchase #4 $213.78   3.403%   $221.0549   $221.05   $221.05   $221.10  
  Purchase #5 $43.65   10.711%   $48.3254   $48.33   $48.35   $48.30  
  Purchase #6 $226.70   6.407%   $241.2247   $241.22   $241.20   $241.20  
  Purchase #7 $44.78   4.725%   $46.8959   $46.90   $46.90   $46.90  
  7 purchase totals = $941.59       $1,009.6172   $1,009.61   $1,009.60   $1,009.60