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 $57.86   13.313%   $65.5629   $65.56   $65.55   $65.60  
  Purchase #2 $5.78   8.180%   $6.2528   $6.25   $6.25   $6.30  
  Purchase #3 $86.81   11.796%   $97.0501   $97.05   $97.05   $97.10  
  Purchase #4 $18.94   6.782%   $20.2245   $20.22   $20.20   $20.20  
  Purchase #5 $59.25   10.579%   $65.5181   $65.52   $65.50   $65.50  
  Purchase #6 $249.51   13.443%   $283.0516   $283.05   $283.05   $283.10  
  Purchase #7 $198.70   13.661%   $225.8444   $225.84   $225.85   $225.80  
  7 purchase totals = $676.85       $763.5044   $763.49   $763.45   $763.60