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 $204.34   10.748%   $226.3025   $226.30   $226.30   $226.30  
  Purchase #2 $183.31   12.207%   $205.6867   $205.69   $205.70   $205.70  
  Purchase #3 $82.27   11.341%   $91.6002   $91.60   $91.60   $91.60  
  Purchase #4 $65.54   4.725%   $68.6368   $68.64   $68.65   $68.60  
  Purchase #5 $9.60   11.858%   $10.7384   $10.74   $10.75   $10.70  
  Purchase #6 $151.25   8.318%   $163.831   $163.83   $163.85   $163.80  
  Purchase #7 $159.29   10.559%   $176.1094   $176.11   $176.10   $176.10  
  7 purchase totals = $855.60       $942.9050   $942.91   $942.95   $942.80