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	$151.89	13.397%	$172.2387	$172.24	$172.25	$172.20
Purchase #2	$116.78	9.809%	$128.235	$128.24	$128.25	$128.20
Purchase #3	$245.75	11.535%	$274.0973	$274.10	$274.10	$274.10
Purchase #4	$161.64	7.162%	$173.2167	$173.22	$173.20	$173.20
Purchase #5	$111.74	11.333%	$124.4035	$124.40	$124.40	$124.40
Purchase #6	$43.60	3.673%	$45.2014	$45.20	$45.20	$45.20
Purchase #7	$151.69	11.773%	$169.5485	$169.55	$169.55	$169.50
7 purchase totals =	$983.09		$1,086.9411	$1,086.95	$1,086.95	$1,086.80