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	$73.59	13.234%	$83.3289	$83.33	$83.35	$83.30
Purchase #2	$118.64	13.108%	$134.1913	$134.19	$134.20	$134.20
Purchase #3	$109.32	13.346%	$123.9098	$123.91	$123.90	$123.90
Purchase #4	$15.70	12.722%	$17.6974	$17.70	$17.70	$17.70
Purchase #5	$53.73	7.418%	$57.7157	$57.72	$57.70	$57.70
Purchase #6	$82.65	12.411%	$92.9077	$92.91	$92.90	$92.90
Purchase #7	$37.89	6.342%	$40.293	$40.29	$40.30	$40.30
7 purchase totals =	$491.52		$550.0438	$550.05	$550.05	$550.00