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 $68.81   11.513%   $76.7321   $76.73   $76.75   $76.70  
  Purchase #2 $134.90   8.580%   $146.4744   $146.47   $146.45   $146.50  
  Purchase #3 $221.72   12.399%   $249.2111   $249.21   $249.20   $249.20  
  Purchase #4 $56.29   4.737%   $58.9565   $58.96   $58.95   $59.00  
  Purchase #5 $151.46   3.185%   $156.284   $156.28   $156.30   $156.30  
  Purchase #6 $225.45   8.684%   $245.0281   $245.03   $245.05   $245.00  
  Purchase #7 $57.27   6.234%   $60.8402   $60.84   $60.85   $60.80  
  7 purchase totals = $915.90       $993.5264   $993.52   $993.55   $993.50