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 $53.95   12.598%   $60.7466   $60.75   $60.75   $60.70  
  Purchase #2 $128.38   5.193%   $135.0468   $135.05   $135.05   $135.00  
  Purchase #3 $58.31   4.833%   $61.1281   $61.13   $61.15   $61.10  
  Purchase #4 $60.92   7.320%   $65.3793   $65.38   $65.40   $65.40  
  Purchase #5 $24.27   8.569%   $26.3497   $26.35   $26.35   $26.30  
  Purchase #6 $133.62   13.655%   $151.8658   $151.87   $151.85   $151.90  
  Purchase #7 $240.82   13.856%   $274.188   $274.19   $274.20   $274.20  
  7 purchase totals = $700.27       $774.7043   $774.72   $774.75   $774.60