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 $195.52   5.526%   $206.3244   $206.32   $206.30   $206.30  
  Purchase #2 $50.26   11.824%   $56.2027   $56.20   $56.20   $56.20  
  Purchase #3 $43.32   10.240%   $47.756   $47.76   $47.75   $47.80  
  Purchase #4 $21.91   4.566%   $22.9104   $22.91   $22.90   $22.90  
  Purchase #5 $49.68   11.480%   $55.3833   $55.38   $55.40   $55.40  
  Purchase #6 $205.35   5.127%   $215.8783   $215.88   $215.90   $215.90  
  Purchase #7 $64.29   13.708%   $73.1029   $73.10   $73.10   $73.10  
  7 purchase totals = $630.33       $677.5580   $677.55   $677.55   $677.60