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 $168.77   9.362%   $184.5702   $184.57   $184.55   $184.60  
  Purchase #2 $238.48   10.420%   $263.3296   $263.33   $263.35   $263.30  
  Purchase #3 $72.27   4.622%   $75.6103   $75.61   $75.60   $75.60  
  Purchase #4 $250.39   10.664%   $277.0916   $277.09   $277.10   $277.10  
  Purchase #5 $182.95   9.226%   $199.829   $199.83   $199.85   $199.80  
  Purchase #6 $57.35   13.621%   $65.1616   $65.16   $65.15   $65.20  
  Purchase #7 $40.86   9.520%   $44.7499   $44.75   $44.75   $44.70  
  7 purchase totals = $1,011.07       $1,110.3422   $1,110.34   $1,110.35   $1,110.30