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 $55.96   11.148%   $62.1984   $62.20   $62.20   $62.20  
  Purchase #2 $60.82   5.616%   $64.2357   $64.24   $64.25   $64.20  
  Purchase #3 $233.77   5.225%   $245.9845   $245.98   $246.00   $246.00  
  Purchase #4 $164.71   7.743%   $177.4635   $177.46   $177.45   $177.50  
  Purchase #5 $46.62   7.786%   $50.2498   $50.25   $50.25   $50.20  
  Purchase #6 $95.52   8.669%   $103.8006   $103.80   $103.80   $103.80  
  Purchase #7 $73.98   10.580%   $81.8071   $81.81   $81.80   $81.80  
  7 purchase totals = $731.38       $785.7396   $785.74   $785.75   $785.70