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 $141.55   13.163%   $160.1822   $160.18   $160.20   $160.20  
  Purchase #2 $55.85   13.746%   $63.5271   $63.53   $63.55   $63.50  
  Purchase #3 $232.93   11.291%   $259.2301   $259.23   $259.25   $259.20  
  Purchase #4 $8.39   10.328%   $9.2565   $9.26   $9.25   $9.30  
  Purchase #5 $221.71   10.200%   $244.3244   $244.32   $244.30   $244.30  
  Purchase #6 $91.36   4.211%   $95.2072   $95.21   $95.20   $95.20  
  Purchase #7 $95.83   10.727%   $106.1097   $106.11   $106.10   $106.10  
  7 purchase totals = $847.62       $937.8372   $937.84   $937.85   $937.80