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 $55.27   5.463%   $58.2894   $58.29   $58.30   $58.30  
  Purchase #2 $136.64   4.250%   $142.4472   $142.45   $142.45   $142.40  
  Purchase #3 $248.53   7.233%   $266.5062   $266.51   $266.50   $266.50  
  Purchase #4 $128.80   9.653%   $141.2331   $141.23   $141.25   $141.20  
  Purchase #5 $217.74   5.817%   $230.4059   $230.41   $230.40   $230.40  
  Purchase #6 $245.28   6.463%   $261.1324   $261.13   $261.15   $261.10  
  Purchase #7 $114.60   6.602%   $122.1659   $122.17   $122.15   $122.20  
  7 purchase totals = $1,146.86       $1,222.1801   $1,222.19   $1,222.20   $1,222.10