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	$17.34	3.160%	$17.8879	$17.89	$17.90	$17.90
Purchase #2	$17.89	5.683%	$18.9067	$18.91	$18.90	$18.90
Purchase #3	$41.86	3.525%	$43.3356	$43.34	$43.35	$43.30
Purchase #4	$6.69	6.739%	$7.1408	$7.14	$7.15	$7.10
Purchase #5	$91.50	11.367%	$101.9008	$101.90	$101.90	$101.90
Purchase #6	$224.42	8.661%	$243.857	$243.86	$243.85	$243.90
Purchase #7	$114.84	8.242%	$124.3051	$124.31	$124.30	$124.30
7 purchase totals =	$514.54		$557.3339	$557.35	$557.35	$557.30