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 $183.95   7.109%   $197.027   $197.03   $197.05   $197.00  
  Purchase #2 $237.90   9.124%   $259.606   $259.61   $259.60   $259.60  
  Purchase #3 $160.57   8.467%   $174.1655   $174.17   $174.15   $174.20  
  Purchase #4 $144.52   13.690%   $164.3048   $164.30   $164.30   $164.30  
  Purchase #5 $244.36   8.552%   $265.2577   $265.26   $265.25   $265.30  
  Purchase #6 $52.84   13.476%   $59.9607   $59.96   $59.95   $60.00  
  Purchase #7 $18.25   3.400%   $18.8705   $18.87   $18.85   $18.90  
  7 purchase totals = $1,042.39       $1,139.1922   $1,139.20   $1,139.15   $1,139.30