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	$144.69	11.418%	$161.2107	$161.21	$161.20	$161.20
Purchase #2	$172.90	10.189%	$190.5168	$190.52	$190.50	$190.50
Purchase #3	$95.33	13.816%	$108.5008	$108.50	$108.50	$108.50
Purchase #4	$154.91	10.744%	$171.5535	$171.55	$171.55	$171.60
Purchase #5	$129.64	13.800%	$147.5303	$147.53	$147.55	$147.50
Purchase #6	$144.61	7.739%	$155.8014	$155.80	$155.80	$155.80
Purchase #7	$241.56	9.355%	$264.1579	$264.16	$264.15	$264.20
7 purchase totals =	$1,083.64		$1,199.2714	$1,199.27	$1,199.25	$1,199.30