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	$127.83	9.658%	$140.1758	$140.18	$140.20	$140.20
Purchase #2	$60.98	10.161%	$67.1762	$67.18	$67.20	$67.20
Purchase #3	$113.72	8.452%	$123.3316	$123.33	$123.35	$123.30
Purchase #4	$238.28	7.568%	$256.313	$256.31	$256.30	$256.30
Purchase #5	$117.64	8.548%	$127.6959	$127.70	$127.70	$127.70
Purchase #6	$185.73	7.481%	$199.6245	$199.62	$199.60	$199.60
Purchase #7	$40.80	9.244%	$44.5716	$44.57	$44.55	$44.60
7 purchase totals =	$884.98		$958.8886	$958.89	$958.90	$958.90