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	$75.66	6.369%	$80.4788	$80.48	$80.50	$80.50
Purchase #2	$216.95	12.685%	$244.4701	$244.47	$244.45	$244.50
Purchase #3	$154.74	3.624%	$160.3478	$160.35	$160.35	$160.30
Purchase #4	$196.80	6.665%	$209.9167	$209.92	$209.90	$209.90
Purchase #5	$172.71	7.302%	$185.3213	$185.32	$185.30	$185.30
Purchase #6	$59.38	11.205%	$66.0335	$66.03	$66.05	$66.00
Purchase #7	$142.39	8.689%	$154.7623	$154.76	$154.75	$154.80
7 purchase totals =	$1,018.63		$1,101.3305	$1,101.33	$1,101.30	$1,101.30