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 $119.71   6.327%   $127.2841   $127.28   $127.30   $127.30  
  Purchase #2 $153.64   5.574%   $162.2039   $162.20   $162.20   $162.20  
  Purchase #3 $173.27   9.373%   $189.5106   $189.51   $189.50   $189.50  
  Purchase #4 $249.49   9.243%   $272.5504   $272.55   $272.55   $272.60  
  Purchase #5 $58.58   8.364%   $63.4796   $63.48   $63.50   $63.50  
  Purchase #6 $156.85   12.210%   $176.0014   $176.00   $176.00   $176.00  
  Purchase #7 $137.73   11.251%   $153.226   $153.23   $153.25   $153.20  
  7 purchase totals = $1,049.27       $1,144.2560   $1,144.25   $1,144.30   $1,144.30