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	$87.52	4.308%	$91.2904	$91.29	$91.30	$91.30
Purchase #2	$38.81	9.356%	$42.4411	$42.44	$42.45	$42.40
Purchase #3	$126.63	3.626%	$131.2216	$131.22	$131.20	$131.20
Purchase #4	$59.46	4.474%	$62.1202	$62.12	$62.10	$62.10
Purchase #5	$126.32	4.531%	$132.0436	$132.04	$132.05	$132.00
Purchase #6	$185.67	5.302%	$195.5142	$195.51	$195.50	$195.50
Purchase #7	$247.29	11.252%	$275.1151	$275.12	$275.10	$275.10
7 purchase totals =	$871.70		$929.7462	$929.74	$929.70	$929.60