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	$171.47	9.213%	$187.2675	$187.27	$187.25	$187.30
Purchase #2	$245.86	11.385%	$273.8512	$273.85	$273.85	$273.90
Purchase #3	$172.96	5.400%	$182.2998	$182.30	$182.30	$182.30
Purchase #4	$85.80	10.418%	$94.7386	$94.74	$94.75	$94.70
Purchase #5	$113.59	12.226%	$127.4775	$127.48	$127.50	$127.50
Purchase #6	$238.79	8.271%	$258.5403	$258.54	$258.55	$258.50
Purchase #7	$184.58	8.500%	$200.2693	$200.27	$200.25	$200.30
7 purchase totals =	$1,213.05		$1,324.4442	$1,324.45	$1,324.45	$1,324.50