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 $95.89   5.244%   $100.9185   $100.92   $100.90   $100.90  
  Purchase #2 $241.78   11.177%   $268.8038   $268.80   $268.80   $268.80  
  Purchase #3 $26.47   12.800%   $29.8582   $29.86   $29.85   $29.90  
  Purchase #4 $44.61   3.554%   $46.1954   $46.20   $46.20   $46.20  
  Purchase #5 $196.37   12.546%   $221.0066   $221.01   $221.00   $221.00  
  Purchase #6 $125.52   10.718%   $138.9732   $138.97   $138.95   $139.00  
  Purchase #7 $52.28   8.513%   $56.7306   $56.73   $56.75   $56.70  
  7 purchase totals = $782.92       $862.4863   $862.49   $862.45   $862.50