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 $206.42   5.260%   $217.2777   $217.28   $217.30   $217.30  
  Purchase #2 $17.39   9.191%   $18.9883   $18.99   $19.00   $19.00  
  Purchase #3 $31.36   7.155%   $33.6038   $33.60   $33.60   $33.60  
  Purchase #4 $91.93   3.693%   $95.325   $95.33   $95.35   $95.30  
  Purchase #5 $104.86   11.493%   $116.9116   $116.91   $116.90   $116.90  
  Purchase #6 $52.63   5.249%   $55.3925   $55.39   $55.40   $55.40  
  Purchase #7 $197.54   4.185%   $205.807   $205.81   $205.80   $205.80  
  7 purchase totals = $702.13       $743.3059   $743.31   $743.35   $743.30