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	$83.87	7.420%	$90.0932	$90.09	$90.10	$90.10
Purchase #2	$103.67	6.692%	$110.6076	$110.61	$110.60	$110.60
Purchase #3	$67.73	8.672%	$73.6035	$73.60	$73.60	$73.60
Purchase #4	$158.43	9.489%	$173.4634	$173.46	$173.45	$173.50
Purchase #5	$188.53	5.723%	$199.3196	$199.32	$199.30	$199.30
Purchase #6	$31.72	12.367%	$35.6428	$35.64	$35.65	$35.60
Purchase #7	$223.29	8.479%	$242.2228	$242.22	$242.20	$242.20
7 purchase totals =	$857.24		$924.9529	$924.94	$924.90	$924.90