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 $178.38   8.767%   $194.0186   $194.02   $194.00   $194.00  
  Purchase #2 $88.87   5.546%   $93.7987   $93.80   $93.80   $93.80  
  Purchase #3 $71.44   4.106%   $74.3733   $74.37   $74.35   $74.40  
  Purchase #4 $137.72   5.691%   $145.5576   $145.56   $145.55   $145.60  
  Purchase #5 $53.85   4.130%   $56.074   $56.07   $56.05   $56.10  
  Purchase #6 $112.98   11.464%   $125.932   $125.93   $125.95   $125.90  
  Purchase #7 $80.40   4.672%   $84.1563   $84.16   $84.15   $84.20  
  7 purchase totals = $723.64       $773.9105   $773.91   $773.85   $774.00