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 $82.57   13.103%   $93.3891   $93.39   $93.40   $93.40  
  Purchase #2 $250.84   8.181%   $271.3612   $271.36   $271.35   $271.40  
  Purchase #3 $46.32   4.759%   $48.5244   $48.52   $48.50   $48.50  
  Purchase #4 $188.53   8.640%   $204.819   $204.82   $204.80   $204.80  
  Purchase #5 $51.57   8.772%   $56.0937   $56.09   $56.10   $56.10  
  Purchase #6 $67.90   6.385%   $72.2354   $72.24   $72.25   $72.20  
  Purchase #7 $16.70   9.451%   $18.2783   $18.28   $18.30   $18.30  
  7 purchase totals = $704.43       $764.7011   $764.70   $764.70   $764.70