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	$92.26	12.201%	$103.5166	$103.52	$103.50	$103.50
Purchase #2	$124.93	7.622%	$134.4522	$134.45	$134.45	$134.50
Purchase #3	$201.36	12.129%	$225.783	$225.78	$225.80	$225.80
Purchase #4	$180.52	8.805%	$196.4148	$196.41	$196.40	$196.40
Purchase #5	$26.41	8.269%	$28.5938	$28.59	$28.60	$28.60
Purchase #6	$83.68	7.222%	$89.7234	$89.72	$89.70	$89.70
Purchase #7	$88.77	11.819%	$99.2617	$99.26	$99.25	$99.30
7 purchase totals =	$797.93		$877.7455	$877.73	$877.70	$877.80