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	$16.69	13.518%	$18.9462	$18.95	$18.95	$18.90
Purchase #2	$165.44	8.868%	$180.1112	$180.11	$180.10	$180.10
Purchase #3	$211.29	11.439%	$235.4595	$235.46	$235.45	$235.50
Purchase #4	$144.96	5.313%	$152.6617	$152.66	$152.65	$152.70
Purchase #5	$172.66	7.486%	$185.5853	$185.59	$185.60	$185.60
Purchase #6	$60.38	8.853%	$65.7254	$65.73	$65.75	$65.70
Purchase #7	$165.50	11.373%	$184.3223	$184.32	$184.30	$184.30
7 purchase totals =	$936.92		$1,022.8116	$1,022.82	$1,022.80	$1,022.80