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 $86.75   13.718%   $98.6504   $98.65   $98.65   $98.70  
  Purchase #2 $28.35   4.579%   $29.6481   $29.65   $29.65   $29.60  
  Purchase #3 $114.80   10.259%   $126.5773   $126.58   $126.60   $126.60  
  Purchase #4 $27.33   6.750%   $29.1748   $29.17   $29.15   $29.20  
  Purchase #5 $40.75   9.492%   $44.618   $44.62   $44.60   $44.60  
  Purchase #6 $194.78   7.494%   $209.3768   $209.38   $209.40   $209.40  
  Purchase #7 $52.30   13.527%   $59.3746   $59.37   $59.35   $59.40  
  7 purchase totals = $545.06       $597.4200   $597.42   $597.40   $597.50