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	$100.33	5.528%	$105.8762	$105.88	$105.90	$105.90
Purchase #2	$95.91	4.437%	$100.1655	$100.17	$100.15	$100.20
Purchase #3	$19.71	10.262%	$21.7326	$21.73	$21.75	$21.70
Purchase #4	$239.45	7.235%	$256.7742	$256.77	$256.75	$256.80
Purchase #5	$243.30	8.690%	$264.4428	$264.44	$264.45	$264.40
Purchase #6	$223.96	5.157%	$235.5096	$235.51	$235.50	$235.50
Purchase #7	$86.48	11.589%	$96.5022	$96.50	$96.50	$96.50
7 purchase totals =	$1,009.14		$1,081.0031	$1,081.00	$1,081.00	$1,081.00