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 $116.26   12.279%   $130.5356   $130.54   $130.55   $130.50  
  Purchase #2 $106.69   9.242%   $116.5503   $116.55   $116.55   $116.60  
  Purchase #3 $136.40   8.433%   $147.9026   $147.90   $147.90   $147.90  
  Purchase #4 $6.62   5.388%   $6.9767   $6.98   $7.00   $7.00  
  Purchase #5 $194.25   13.511%   $220.4951   $220.50   $220.50   $220.50  
  Purchase #6 $11.48   9.205%   $12.5367   $12.54   $12.55   $12.50  
  Purchase #7 $110.87   12.318%   $124.527   $124.53   $124.55   $124.50  
  7 purchase totals = $682.57       $759.5240   $759.54   $759.60   $759.50