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 $247.47   10.747%   $274.0656   $274.07   $274.05   $274.10  
  Purchase #2 $47.60   10.701%   $52.6937   $52.69   $52.70   $52.70  
  Purchase #3 $87.46   5.828%   $92.5572   $92.56   $92.55   $92.60  
  Purchase #4 $26.77   10.833%   $29.67   $29.67   $29.65   $29.70  
  Purchase #5 $172.39   7.762%   $185.7709   $185.77   $185.75   $185.80  
  Purchase #6 $230.95   13.124%   $261.2599   $261.26   $261.25   $261.30  
  Purchase #7 $144.48   4.199%   $150.5467   $150.55   $150.55   $150.50  
  7 purchase totals = $957.12       $1,046.5640   $1,046.57   $1,046.50   $1,046.70