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	$244.99	3.425%	$253.3809	$253.38	$253.40	$253.40
Purchase #2	$73.77	9.444%	$80.7368	$80.74	$80.75	$80.70
Purchase #3	$237.66	7.131%	$254.6075	$254.61	$254.60	$254.60
Purchase #4	$228.67	5.221%	$240.6089	$240.61	$240.60	$240.60
Purchase #5	$41.32	10.739%	$45.7574	$45.76	$45.75	$45.80
Purchase #6	$171.36	12.485%	$192.7543	$192.75	$192.75	$192.80
Purchase #7	$30.56	3.388%	$31.5954	$31.60	$31.60	$31.60
7 purchase totals =	$1,028.33		$1,099.4412	$1,099.45	$1,099.45	$1,099.50