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 $76.60   10.468%   $84.6185   $84.62   $84.60   $84.60  
  Purchase #2 $133.95   10.736%   $148.3309   $148.33   $148.35   $148.30  
  Purchase #3 $196.69   8.478%   $213.3654   $213.37   $213.35   $213.40  
  Purchase #4 $221.37   5.493%   $233.5299   $233.53   $233.55   $233.50  
  Purchase #5 $87.26   7.433%   $93.746   $93.75   $93.75   $93.70  
  Purchase #6 $222.69   5.416%   $234.7509   $234.75   $234.75   $234.80  
  Purchase #7 $246.31   4.801%   $258.1353   $258.14   $258.15   $258.10  
  7 purchase totals = $1,184.87       $1,266.4769   $1,266.49   $1,266.50   $1,266.40