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 $175.68   12.171%   $197.062   $197.06   $197.05   $197.10  
  Purchase #2 $14.85   3.730%   $15.4039   $15.40   $15.40   $15.40  
  Purchase #3 $172.33   6.350%   $183.273   $183.27   $183.25   $183.30  
  Purchase #4 $149.86   12.606%   $168.7514   $168.75   $168.75   $168.80  
  Purchase #5 $76.91   9.397%   $84.1372   $84.14   $84.15   $84.10  
  Purchase #6 $33.25   11.684%   $37.1349   $37.13   $37.15   $37.10  
  Purchase #7 $248.72   4.332%   $259.4946   $259.49   $259.50   $259.50  
  7 purchase totals = $871.60       $945.2570   $945.24   $945.25   $945.30