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	$84.27	6.388%	$89.6532	$89.65	$89.65	$89.70
Purchase #2	$89.76	12.230%	$100.7376	$100.74	$100.75	$100.70
Purchase #3	$83.77	5.383%	$88.2793	$88.28	$88.30	$88.30
Purchase #4	$69.62	5.413%	$73.3885	$73.39	$73.40	$73.40
Purchase #5	$154.76	13.792%	$176.1045	$176.10	$176.10	$176.10
Purchase #6	$91.51	9.219%	$99.9463	$99.95	$99.95	$99.90
Purchase #7	$236.56	9.134%	$258.1674	$258.17	$258.15	$258.20
7 purchase totals =	$810.25		$886.2768	$886.28	$886.30	$886.30