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	$157.39	4.338%	$164.2176	$164.22	$164.20	$164.20
Purchase #2	$45.66	10.518%	$50.4625	$50.46	$50.45	$50.50
Purchase #3	$153.59	3.720%	$159.3035	$159.30	$159.30	$159.30
Purchase #4	$74.66	12.386%	$83.9074	$83.91	$83.90	$83.90
Purchase #5	$226.27	9.843%	$248.5418	$248.54	$248.55	$248.50
Purchase #6	$235.93	7.383%	$253.3487	$253.35	$253.35	$253.30
Purchase #7	$149.79	12.635%	$168.716	$168.72	$168.70	$168.70
7 purchase totals =	$1,043.29		$1,128.4975	$1,128.50	$1,128.45	$1,128.40