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 $52.56   13.261%   $59.53   $59.53   $59.55   $59.50  
  Purchase #2 $218.57   13.440%   $247.9458   $247.95   $247.95   $247.90  
  Purchase #3 $108.42   13.394%   $122.9418   $122.94   $122.95   $122.90  
  Purchase #4 $57.70   7.356%   $61.9444   $61.94   $61.95   $61.90  
  Purchase #5 $76.47   10.441%   $84.4542   $84.45   $84.45   $84.50  
  Purchase #6 $180.73   9.683%   $198.2301   $198.23   $198.25   $198.20  
  Purchase #7 $215.49   10.112%   $237.2803   $237.28   $237.30   $237.30  
  7 purchase totals = $909.94       $1,012.3266   $1,012.32   $1,012.40   $1,012.20