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 $88.30   10.204%   $97.3101   $97.31   $97.30   $97.30  
  Purchase #2 $57.93   10.153%   $63.8116   $63.81   $63.80   $63.80  
  Purchase #3 $166.56   4.295%   $173.7138   $173.71   $173.70   $173.70  
  Purchase #4 $110.76   10.376%   $122.2525   $122.25   $122.25   $122.30  
  Purchase #5 $71.61   8.714%   $77.8501   $77.85   $77.85   $77.90  
  Purchase #6 $5.37   11.227%   $5.9729   $5.97   $5.95   $6.00  
  Purchase #7 $236.39   11.260%   $263.0075   $263.01   $263.00   $263.00  
  7 purchase totals = $736.92       $803.9185   $803.91   $803.85   $804.00