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 $41.91   6.327%   $44.5616   $44.56   $44.55   $44.60  
  Purchase #2 $92.74   6.634%   $98.8924   $98.89   $98.90   $98.90  
  Purchase #3 $86.27   8.488%   $93.5926   $93.59   $93.60   $93.60  
  Purchase #4 $103.56   9.813%   $113.7223   $113.72   $113.70   $113.70  
  Purchase #5 $137.84   3.351%   $142.459   $142.46   $142.45   $142.50  
  Purchase #6 $197.86   8.105%   $213.8966   $213.90   $213.90   $213.90  
  Purchase #7 $71.25   4.504%   $74.4591   $74.46   $74.45   $74.50  
  7 purchase totals = $731.43       $781.5836   $781.58   $781.55   $781.70