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 $199.51   8.673%   $216.8135   $216.81   $216.80   $216.80  
  Purchase #2 $95.49   3.598%   $98.9257   $98.93   $98.95   $98.90  
  Purchase #3 $140.35   3.207%   $144.851   $144.85   $144.85   $144.90  
  Purchase #4 $147.26   6.438%   $156.7406   $156.74   $156.75   $156.70  
  Purchase #5 $65.67   6.860%   $70.175   $70.18   $70.20   $70.20  
  Purchase #6 $46.38   9.121%   $50.6103   $50.61   $50.60   $50.60  
  Purchase #7 $26.48   12.276%   $29.7307   $29.73   $29.75   $29.70  
  7 purchase totals = $721.14       $767.8468   $767.85   $767.90   $767.80