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 $119.61   8.436%   $129.7003   $129.70   $129.70   $129.70  
  Purchase #2 $124.48   10.663%   $137.7533   $137.75   $137.75   $137.80  
  Purchase #3 $213.76   12.761%   $241.0379   $241.04   $241.05   $241.00  
  Purchase #4 $177.59   12.142%   $199.153   $199.15   $199.15   $199.20  
  Purchase #5 $51.83   7.268%   $55.597   $55.60   $55.60   $55.60  
  Purchase #6 $180.99   13.487%   $205.4001   $205.40   $205.40   $205.40  
  Purchase #7 $206.31   4.291%   $215.1628   $215.16   $215.15   $215.20  
  7 purchase totals = $1,074.57       $1,183.8044   $1,183.80   $1,183.80   $1,183.90