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 $167.86   13.762%   $190.9609   $190.96   $190.95   $191.00  
  Purchase #2 $49.26   11.531%   $54.9402   $54.94   $54.95   $54.90  
  Purchase #3 $17.88   10.615%   $19.778   $19.78   $19.80   $19.80  
  Purchase #4 $56.57   6.537%   $60.268   $60.27   $60.25   $60.30  
  Purchase #5 $220.97   12.514%   $248.6222   $248.62   $248.60   $248.60  
  Purchase #6 $47.73   4.292%   $49.7786   $49.78   $49.80   $49.80  
  Purchase #7 $104.73   13.457%   $118.8235   $118.82   $118.80   $118.80  
  7 purchase totals = $665.00       $743.1714   $743.17   $743.15   $743.20