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 $83.57   6.212%   $88.7614   $88.76   $88.75   $88.80  
  Purchase #2 $176.29   4.870%   $184.8753   $184.88   $184.90   $184.90  
  Purchase #3 $104.30   10.208%   $114.9469   $114.95   $114.95   $114.90  
  Purchase #4 $226.86   9.445%   $248.2869   $248.29   $248.30   $248.30  
  Purchase #5 $158.50   4.722%   $165.9844   $165.98   $166.00   $166.00  
  Purchase #6 $120.73   3.434%   $124.8759   $124.88   $124.90   $124.90  
  Purchase #7 $70.74   5.770%   $74.8217   $74.82   $74.80   $74.80  
  7 purchase totals = $940.99       $1,002.5525   $1,002.56   $1,002.60   $1,002.60