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 $142.91   11.452%   $159.2761   $159.28   $159.30   $159.30  
  Purchase #2 $59.42   9.858%   $65.2776   $65.28   $65.30   $65.30  
  Purchase #3 $234.62   5.493%   $247.5077   $247.51   $247.50   $247.50  
  Purchase #4 $31.47   9.547%   $34.4744   $34.47   $34.45   $34.50  
  Purchase #5 $22.29   11.719%   $24.9022   $24.90   $24.90   $24.90  
  Purchase #6 $43.36   12.450%   $48.7583   $48.76   $48.75   $48.80  
  Purchase #7 $176.74   5.633%   $186.6958   $186.70   $186.70   $186.70  
  7 purchase totals = $710.81       $766.8921   $766.90   $766.90   $767.00