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	$135.95	6.329%	$144.5543	$144.55	$144.55	$144.60
Purchase #2	$38.28	10.483%	$42.2929	$42.29	$42.30	$42.30
Purchase #3	$173.30	10.637%	$191.7339	$191.73	$191.75	$191.70
Purchase #4	$128.87	11.392%	$143.5509	$143.55	$143.55	$143.60
Purchase #5	$84.61	4.844%	$88.7085	$88.71	$88.70	$88.70
Purchase #6	$138.34	6.142%	$146.8368	$146.84	$146.85	$146.80
Purchase #7	$123.73	12.649%	$139.3806	$139.38	$139.40	$139.40
7 purchase totals =	$823.08		$897.0579	$897.05	$897.10	$897.10