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	$108.93	13.267%	$123.3817	$123.38	$123.40	$123.40
Purchase #2	$54.85	13.518%	$62.2646	$62.26	$62.25	$62.30
Purchase #3	$182.33	13.222%	$206.4377	$206.44	$206.45	$206.40
Purchase #4	$49.62	10.660%	$54.9095	$54.91	$54.90	$54.90
Purchase #5	$231.87	12.697%	$261.3105	$261.31	$261.30	$261.30
Purchase #6	$250.73	9.765%	$275.2138	$275.21	$275.20	$275.20
Purchase #7	$104.87	10.134%	$115.4975	$115.50	$115.50	$115.50
7 purchase totals =	$983.20		$1,099.0153	$1,099.01	$1,099.00	$1,099.00