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	$38.89	4.792%	$40.7536	$40.75	$40.75	$40.80
Purchase #2	$32.68	8.254%	$35.3774	$35.38	$35.40	$35.40
Purchase #3	$85.81	3.160%	$88.5216	$88.52	$88.50	$88.50
Purchase #4	$194.52	11.116%	$216.1428	$216.14	$216.15	$216.10
Purchase #5	$64.63	13.797%	$73.547	$73.55	$73.55	$73.50
Purchase #6	$29.90	10.546%	$33.0533	$33.05	$33.05	$33.10
Purchase #7	$134.45	9.532%	$147.2658	$147.27	$147.25	$147.30
7 purchase totals =	$580.88		$634.6615	$634.66	$634.65	$634.70