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 $88.72   7.777%   $95.6198   $95.62   $95.60   $95.60  
  Purchase #2 $19.99   3.226%   $20.6349   $20.63   $20.65   $20.60  
  Purchase #3 $59.37   7.846%   $64.0282   $64.03   $64.05   $64.00  
  Purchase #4 $74.32   13.792%   $84.5702   $84.57   $84.55   $84.60  
  Purchase #5 $113.72   4.572%   $118.9193   $118.92   $118.90   $118.90  
  Purchase #6 $250.85   3.794%   $260.3672   $260.37   $260.35   $260.40  
  Purchase #7 $167.92   6.283%   $178.4704   $178.47   $178.45   $178.50  
  7 purchase totals = $774.89       $822.6100   $822.61   $822.55   $822.60