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 $215.44   3.838%   $223.7086   $223.71   $223.70   $223.70  
  Purchase #2 $56.33   4.666%   $58.9584   $58.96   $58.95   $59.00  
  Purchase #3 $206.64   7.250%   $221.6214   $221.62   $221.60   $221.60  
  Purchase #4 $5.57   3.321%   $5.755   $5.76   $5.75   $5.80  
  Purchase #5 $56.90   6.109%   $60.376   $60.38   $60.40   $60.40  
  Purchase #6 $106.26   9.439%   $116.2899   $116.29   $116.30   $116.30  
  Purchase #7 $104.70   9.570%   $114.7198   $114.72   $114.70   $114.70  
  7 purchase totals = $751.84       $801.4291   $801.44   $801.40   $801.50