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	$46.70	11.696%	$52.162	$52.16	$52.15	$52.20
Purchase #2	$139.84	11.297%	$155.6377	$155.64	$155.65	$155.60
Purchase #3	$145.50	4.478%	$152.0155	$152.02	$152.00	$152.00
Purchase #4	$159.29	8.570%	$172.9412	$172.94	$172.95	$172.90
Purchase #5	$50.71	12.277%	$56.9357	$56.94	$56.95	$56.90
Purchase #6	$111.78	3.304%	$115.4732	$115.47	$115.45	$115.50
Purchase #7	$235.53	6.474%	$250.7782	$250.78	$250.80	$250.80
7 purchase totals =	$889.35		$955.9435	$955.95	$955.95	$955.90