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 $76.29   12.186%   $85.5867   $85.59   $85.60   $85.60  
  Purchase #2 $105.49   8.386%   $114.3364   $114.34   $114.35   $114.30  
  Purchase #3 $24.65   13.288%   $27.9255   $27.93   $27.95   $27.90  
  Purchase #4 $86.87   5.754%   $91.8685   $91.87   $91.85   $91.90  
  Purchase #5 $180.45   8.476%   $195.7449   $195.74   $195.75   $195.70  
  Purchase #6 $241.39   9.838%   $265.1379   $265.14   $265.15   $265.10  
  Purchase #7 $209.90   13.531%   $238.3016   $238.30   $238.30   $238.30  
  7 purchase totals = $925.04       $1,018.9015   $1,018.91   $1,018.95   $1,018.80