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 $216.48   13.481%   $245.6637   $245.66   $245.65   $245.70  
  Purchase #2 $10.40   12.406%   $11.6902   $11.69   $11.70   $11.70  
  Purchase #3 $150.92   12.596%   $169.9299   $169.93   $169.95   $169.90  
  Purchase #4 $210.51   6.370%   $223.9195   $223.92   $223.90   $223.90  
  Purchase #5 $231.53   7.244%   $248.302   $248.30   $248.30   $248.30  
  Purchase #6 $246.32   11.552%   $274.7749   $274.77   $274.75   $274.80  
  Purchase #7 $227.39   7.722%   $244.9491   $244.95   $244.95   $244.90  
  7 purchase totals = $1,293.55       $1,419.2293   $1,419.22   $1,419.20   $1,419.20