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 $65.52   12.197%   $73.5115   $73.51   $73.50   $73.50  
  Purchase #2 $102.93   5.281%   $108.3657   $108.37   $108.35   $108.40  
  Purchase #3 $109.52   13.127%   $123.8967   $123.90   $123.90   $123.90  
  Purchase #4 $132.75   10.335%   $146.4697   $146.47   $146.45   $146.50  
  Purchase #5 $182.29   6.474%   $194.0915   $194.09   $194.10   $194.10  
  Purchase #6 $14.33   12.548%   $16.1281   $16.13   $16.15   $16.10  
  Purchase #7 $110.83   3.785%   $115.0249   $115.02   $115.00   $115.00  
  7 purchase totals = $718.17       $777.4881   $777.49   $777.45   $777.50