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 $90.57   8.522%   $98.2884   $98.29   $98.30   $98.30  
  Purchase #2 $102.82   11.752%   $114.9034   $114.90   $114.90   $114.90  
  Purchase #3 $187.40   13.634%   $212.9501   $212.95   $212.95   $213.00  
  Purchase #4 $162.70   12.645%   $183.2734   $183.27   $183.25   $183.30  
  Purchase #5 $40.63   11.575%   $45.3329   $45.33   $45.35   $45.30  
  Purchase #6 $237.58   9.621%   $260.4376   $260.44   $260.45   $260.40  
  Purchase #7 $85.63   8.643%   $93.031   $93.03   $93.05   $93.00  
  7 purchase totals = $907.33       $1,008.2168   $1,008.21   $1,008.25   $1,008.20