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	$94.45	5.578%	$99.7184	$99.72	$99.70	$99.70
Purchase #2	$34.63	12.541%	$38.9729	$38.97	$38.95	$39.00
Purchase #3	$236.89	5.757%	$250.5278	$250.53	$250.55	$250.50
Purchase #4	$136.73	12.257%	$153.489	$153.49	$153.50	$153.50
Purchase #5	$96.57	9.205%	$105.4593	$105.46	$105.45	$105.50
Purchase #6	$125.52	7.299%	$134.6817	$134.68	$134.70	$134.70
Purchase #7	$79.30	12.871%	$89.5067	$89.51	$89.50	$89.50
7 purchase totals =	$804.09		$872.3558	$872.36	$872.35	$872.40