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	$219.74	10.810%	$243.4939	$243.49	$243.50	$243.50
Purchase #2	$114.81	3.337%	$118.6412	$118.64	$118.65	$118.60
Purchase #3	$212.29	6.401%	$225.8787	$225.88	$225.90	$225.90
Purchase #4	$94.70	9.729%	$103.9134	$103.91	$103.90	$103.90
Purchase #5	$60.52	13.560%	$68.7265	$68.73	$68.75	$68.70
Purchase #6	$76.67	8.854%	$83.4584	$83.46	$83.45	$83.50
Purchase #7	$40.76	11.735%	$45.5432	$45.54	$45.55	$45.50
7 purchase totals =	$819.49		$889.6553	$889.65	$889.70	$889.60