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 $241.33   9.862%   $265.13   $265.13   $265.15   $265.10  
  Purchase #2 $63.29   5.235%   $66.6032   $66.60   $66.60   $66.60  
  Purchase #3 $84.75   12.711%   $95.5226   $95.52   $95.50   $95.50  
  Purchase #4 $39.47   13.867%   $44.9433   $44.94   $44.95   $44.90  
  Purchase #5 $235.69   5.800%   $249.36   $249.36   $249.35   $249.40  
  Purchase #6 $93.78   12.629%   $105.6235   $105.62   $105.60   $105.60  
  Purchase #7 $73.39   7.641%   $78.9977   $79.00   $79.00   $79.00  
  7 purchase totals = $831.70       $906.1803   $906.17   $906.15   $906.10