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 $156.33   8.261%   $169.2444   $169.24   $169.25   $169.20  
  Purchase #2 $62.73   6.228%   $66.6368   $66.64   $66.65   $66.60  
  Purchase #3 $230.93   9.213%   $252.2056   $252.21   $252.20   $252.20  
  Purchase #4 $219.40   5.868%   $232.2744   $232.27   $232.25   $232.30  
  Purchase #5 $190.75   12.279%   $214.1722   $214.17   $214.15   $214.20  
  Purchase #6 $248.92   8.851%   $270.9519   $270.95   $270.95   $271.00  
  Purchase #7 $158.26   10.114%   $174.2664   $174.27   $174.25   $174.30  
  7 purchase totals = $1,267.32       $1,379.7517   $1,379.75   $1,379.70   $1,379.80