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 $89.89   5.664%   $94.9814   $94.98   $95.00   $95.00  
  Purchase #2 $39.95   12.108%   $44.7871   $44.79   $44.80   $44.80  
  Purchase #3 $150.72   4.308%   $157.213   $157.21   $157.20   $157.20  
  Purchase #4 $98.38   10.372%   $108.584   $108.58   $108.60   $108.60  
  Purchase #5 $71.88   8.218%   $77.7871   $77.79   $77.80   $77.80  
  Purchase #6 $187.59   10.685%   $207.634   $207.63   $207.65   $207.60  
  Purchase #7 $90.53   8.261%   $98.0087   $98.01   $98.00   $98.00  
  7 purchase totals = $728.94       $788.9953   $788.99   $789.05   $789.00