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	$248.48	8.614%	$269.8841	$269.88	$269.90	$269.90
Purchase #2	$134.42	6.712%	$143.4423	$143.44	$143.45	$143.40
Purchase #3	$154.55	11.301%	$172.0157	$172.02	$172.00	$172.00
Purchase #4	$99.58	5.181%	$104.7392	$104.74	$104.75	$104.70
Purchase #5	$137.97	7.205%	$147.9107	$147.91	$147.90	$147.90
Purchase #6	$52.55	5.700%	$55.5454	$55.55	$55.55	$55.50
Purchase #7	$241.60	7.179%	$258.9445	$258.94	$258.95	$258.90
7 purchase totals =	$1,069.15		$1,152.4819	$1,152.48	$1,152.50	$1,152.30