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 $238.93   9.647%   $261.9796   $261.98   $262.00   $262.00  
  Purchase #2 $27.46   4.575%   $28.7163   $28.72   $28.70   $28.70  
  Purchase #3 $51.43   10.468%   $56.8137   $56.81   $56.80   $56.80  
  Purchase #4 $206.76   6.657%   $220.524   $220.52   $220.50   $220.50  
  Purchase #5 $58.65   3.337%   $60.6072   $60.61   $60.60   $60.60  
  Purchase #6 $89.85   11.657%   $100.3238   $100.32   $100.30   $100.30  
  Purchase #7 $217.65   7.533%   $234.0456   $234.05   $234.05   $234.00  
  7 purchase totals = $890.73       $963.0102   $963.01   $962.95   $962.90