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	$123.69	3.607%	$128.1515	$128.15	$128.15	$128.20
Purchase #2	$219.68	10.135%	$241.9446	$241.94	$241.95	$241.90
Purchase #3	$133.28	13.612%	$151.4221	$151.42	$151.40	$151.40
Purchase #4	$85.88	11.824%	$96.0345	$96.03	$96.05	$96.00
Purchase #5	$243.41	13.664%	$276.6695	$276.67	$276.65	$276.70
Purchase #6	$56.66	5.740%	$59.9123	$59.91	$59.90	$59.90
Purchase #7	$146.39	8.128%	$158.2886	$158.29	$158.30	$158.30
7 purchase totals =	$1,008.99		$1,112.4231	$1,112.41	$1,112.40	$1,112.40