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	$47.53	4.611%	$49.7216	$49.72	$49.70	$49.70
Purchase #2	$31.34	6.309%	$33.3172	$33.32	$33.30	$33.30
Purchase #3	$95.57	4.790%	$100.1478	$100.15	$100.15	$100.10
Purchase #4	$69.50	5.640%	$73.4198	$73.42	$73.40	$73.40
Purchase #5	$173.64	8.628%	$188.6217	$188.62	$188.60	$188.60
Purchase #6	$144.28	3.844%	$149.8261	$149.83	$149.85	$149.80
Purchase #7	$198.76	11.852%	$222.317	$222.32	$222.30	$222.30
7 purchase totals =	$760.62		$817.3712	$817.38	$817.30	$817.20