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 $206.47   9.614%   $226.32   $226.32   $226.30   $226.30  
  Purchase #2 $214.47   7.305%   $230.137   $230.14   $230.15   $230.10  
  Purchase #3 $116.45   10.870%   $129.1081   $129.11   $129.10   $129.10  
  Purchase #4 $45.88   6.632%   $48.9228   $48.92   $48.90   $48.90  
  Purchase #5 $168.96   6.747%   $180.3597   $180.36   $180.35   $180.40  
  Purchase #6 $167.50   10.871%   $185.7089   $185.71   $185.70   $185.70  
  Purchase #7 $42.97   11.486%   $47.9055   $47.91   $47.90   $47.90  
  7 purchase totals = $962.70       $1,048.4620   $1,048.47   $1,048.40   $1,048.40