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 $152.88   10.699%   $169.2366   $169.24   $169.25   $169.20  
  Purchase #2 $248.72   12.319%   $279.3598   $279.36   $279.35   $279.40  
  Purchase #3 $144.92   4.402%   $151.2994   $151.30   $151.30   $151.30  
  Purchase #4 $175.65   13.581%   $199.505   $199.51   $199.50   $199.50  
  Purchase #5 $200.27   8.268%   $216.8283   $216.83   $216.85   $216.80  
  Purchase #6 $217.91   3.618%   $225.794   $225.79   $225.80   $225.80  
  Purchase #7 $153.91   8.287%   $166.6645   $166.66   $166.65   $166.70  
  7 purchase totals = $1,294.26       $1,408.6876   $1,408.69   $1,408.70   $1,408.70