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 $93.68   5.697%   $99.0169   $99.02   $99.00   $99.00  
  Purchase #2 $168.87   6.852%   $180.441   $180.44   $180.45   $180.40  
  Purchase #3 $76.83   6.571%   $81.8785   $81.88   $81.90   $81.90  
  Purchase #4 $156.99   7.843%   $169.3027   $169.30   $169.30   $169.30  
  Purchase #5 $14.43   11.304%   $16.0612   $16.06   $16.05   $16.10  
  Purchase #6 $94.89   9.193%   $103.6132   $103.61   $103.60   $103.60  
  Purchase #7 $156.35   11.621%   $174.5194   $174.52   $174.50   $174.50  
  7 purchase totals = $762.04       $824.8329   $824.83   $824.80   $824.80