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	$64.89	8.712%	$70.5432	$70.54	$70.55	$70.50
Purchase #2	$72.67	3.817%	$75.4438	$75.44	$75.45	$75.40
Purchase #3	$230.57	8.322%	$249.758	$249.76	$249.75	$249.80
Purchase #4	$147.28	8.187%	$159.3378	$159.34	$159.35	$159.30
Purchase #5	$35.43	8.788%	$38.5436	$38.54	$38.55	$38.50
Purchase #6	$106.95	5.583%	$112.921	$112.92	$112.90	$112.90
Purchase #7	$118.56	4.494%	$123.8881	$123.89	$123.90	$123.90
7 purchase totals =	$776.35		$830.4355	$830.43	$830.45	$830.30