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	$217.72	9.789%	$239.0326	$239.03	$239.05	$239.00
Purchase #2	$46.45	7.753%	$50.0513	$50.05	$50.05	$50.10
Purchase #3	$134.38	11.657%	$150.0447	$150.04	$150.05	$150.00
Purchase #4	$152.76	3.675%	$158.3739	$158.37	$158.35	$158.40
Purchase #5	$79.79	11.728%	$89.1478	$89.15	$89.15	$89.10
Purchase #6	$78.91	11.777%	$88.2032	$88.20	$88.20	$88.20
Purchase #7	$122.73	13.574%	$139.3894	$139.39	$139.40	$139.40
7 purchase totals =	$832.74		$914.2429	$914.23	$914.25	$914.20