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 $208.74   6.598%   $222.5127   $222.51   $222.50   $222.50  
  Purchase #2 $188.41   13.378%   $213.6155   $213.62   $213.60   $213.60  
  Purchase #3 $214.58   12.754%   $241.9475   $241.95   $241.95   $241.90  
  Purchase #4 $200.99   13.636%   $228.397   $228.40   $228.40   $228.40  
  Purchase #5 $219.67   11.206%   $244.2862   $244.29   $244.30   $244.30  
  Purchase #6 $58.94   13.496%   $66.8945   $66.89   $66.90   $66.90  
  Purchase #7 $187.78   5.327%   $197.783   $197.78   $197.80   $197.80  
  7 purchase totals = $1,279.11       $1,415.4364   $1,415.44   $1,415.45   $1,415.40