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	$78.44	5.145%	$82.4757	$82.48	$82.50	$82.50
Purchase #2	$118.48	13.327%	$134.2698	$134.27	$134.25	$134.30
Purchase #3	$221.56	11.549%	$247.148	$247.15	$247.15	$247.10
Purchase #4	$140.82	4.612%	$147.3146	$147.31	$147.30	$147.30
Purchase #5	$134.85	12.567%	$151.7966	$151.80	$151.80	$151.80
Purchase #6	$189.69	13.763%	$215.797	$215.80	$215.80	$215.80
Purchase #7	$211.34	12.728%	$238.2394	$238.24	$238.25	$238.20
7 purchase totals =	$1,095.18		$1,217.0411	$1,217.05	$1,217.05	$1,217.00