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 $86.27   13.621%   $98.0208   $98.02   $98.00   $98.00  
  Purchase #2 $69.99   7.602%   $75.3106   $75.31   $75.30   $75.30  
  Purchase #3 $12.59   4.844%   $13.1999   $13.20   $13.20   $13.20  
  Purchase #4 $73.36   13.110%   $82.9775   $82.98   $83.00   $83.00  
  Purchase #5 $124.86   12.618%   $140.6148   $140.61   $140.60   $140.60  
  Purchase #6 $42.52   11.381%   $47.3592   $47.36   $47.35   $47.40  
  Purchase #7 $119.80   9.210%   $130.8336   $130.83   $130.85   $130.80  
  7 purchase totals = $529.39       $588.3164   $588.31   $588.30   $588.30