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 $248.48   9.430%   $271.9117   $271.91   $271.90   $271.90  
  Purchase #2 $158.67   7.199%   $170.0927   $170.09   $170.10   $170.10  
  Purchase #3 $11.43   8.185%   $12.3655   $12.37   $12.35   $12.40  
  Purchase #4 $26.73   4.478%   $27.927   $27.93   $27.95   $27.90  
  Purchase #5 $78.65   5.469%   $82.9514   $82.95   $82.95   $83.00  
  Purchase #6 $189.81   3.550%   $196.5483   $196.55   $196.55   $196.50  
  Purchase #7 $169.30   13.735%   $192.5534   $192.55   $192.55   $192.60  
  7 purchase totals = $883.07       $954.3500   $954.35   $954.35   $954.40