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 $59.86   11.345%   $66.6511   $66.65   $66.65   $66.70  
  Purchase #2 $240.34   5.672%   $253.9721   $253.97   $253.95   $254.00  
  Purchase #3 $93.46   4.853%   $97.9956   $98.00   $98.00   $98.00  
  Purchase #4 $60.72   12.796%   $68.4897   $68.49   $68.50   $68.50  
  Purchase #5 $77.75   6.410%   $82.7338   $82.73   $82.75   $82.70  
  Purchase #6 $246.52   9.829%   $270.7505   $270.75   $270.75   $270.80  
  Purchase #7 $15.76   3.804%   $16.3595   $16.36   $16.35   $16.40  
  7 purchase totals = $794.41       $856.9523   $856.95   $856.95   $857.10