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 $32.75   6.573%   $34.9027   $34.90   $34.90   $34.90  
  Purchase #2 $245.51   8.855%   $267.2499   $267.25   $267.25   $267.20  
  Purchase #3 $113.64   6.500%   $121.0266   $121.03   $121.05   $121.00  
  Purchase #4 $166.36   6.657%   $177.4346   $177.43   $177.45   $177.40  
  Purchase #5 $63.84   9.603%   $69.9706   $69.97   $69.95   $70.00  
  Purchase #6 $72.27   5.116%   $75.9673   $75.97   $75.95   $76.00  
  Purchase #7 $68.65   6.292%   $72.9695   $72.97   $72.95   $73.00  
  7 purchase totals = $763.02       $819.5212   $819.52   $819.50   $819.50