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 $53.68   3.108%   $55.3484   $55.35   $55.35   $55.30  
  Purchase #2 $92.53   6.874%   $98.8905   $98.89   $98.90   $98.90  
  Purchase #3 $206.94   9.335%   $226.2578   $226.26   $226.25   $226.30  
  Purchase #4 $137.67   6.786%   $147.0123   $147.01   $147.00   $147.00  
  Purchase #5 $243.41   8.438%   $263.9489   $263.95   $263.95   $263.90  
  Purchase #6 $234.97   3.872%   $244.068   $244.07   $244.05   $244.10  
  Purchase #7 $214.64   9.211%   $234.4105   $234.41   $234.40   $234.40  
  7 purchase totals = $1,183.84       $1,269.9364   $1,269.94   $1,269.90   $1,269.90