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	$33.78	4.154%	$35.1832	$35.18	$35.20	$35.20
Purchase #2	$73.33	7.238%	$78.6376	$78.64	$78.65	$78.60
Purchase #3	$55.68	9.756%	$61.1121	$61.11	$61.10	$61.10
Purchase #4	$161.47	4.849%	$169.2997	$169.30	$169.30	$169.30
Purchase #5	$89.67	5.569%	$94.6637	$94.66	$94.65	$94.70
Purchase #6	$133.89	13.816%	$152.3882	$152.39	$152.40	$152.40
Purchase #7	$44.85	6.667%	$47.8401	$47.84	$47.85	$47.80
7 purchase totals =	$592.67		$639.1246	$639.12	$639.15	$639.10