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	$17.46	13.188%	$19.7626	$19.76	$19.75	$19.80
Purchase #2	$118.75	9.737%	$130.3127	$130.31	$130.30	$130.30
Purchase #3	$70.55	11.164%	$78.4262	$78.43	$78.45	$78.40
Purchase #4	$58.84	11.281%	$65.4777	$65.48	$65.50	$65.50
Purchase #5	$234.78	3.512%	$243.0255	$243.03	$243.05	$243.00
Purchase #6	$6.69	10.519%	$7.3937	$7.39	$7.40	$7.40
Purchase #7	$249.86	13.761%	$284.2432	$284.24	$284.25	$284.20
7 purchase totals =	$756.93		$828.6416	$828.64	$828.70	$828.60