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	$148.29	7.783%	$159.8314	$159.83	$159.85	$159.80
Purchase #2	$82.69	3.427%	$85.5238	$85.52	$85.50	$85.50
Purchase #3	$116.39	12.298%	$130.7036	$130.70	$130.70	$130.70
Purchase #4	$162.33	10.812%	$179.8811	$179.88	$179.90	$179.90
Purchase #5	$11.95	4.740%	$12.5164	$12.52	$12.50	$12.50
Purchase #6	$113.84	12.842%	$128.4593	$128.46	$128.45	$128.50
Purchase #7	$107.37	5.178%	$112.9296	$112.93	$112.95	$112.90
7 purchase totals =	$742.86		$809.8452	$809.84	$809.85	$809.80