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	$166.52	8.399%	$180.506	$180.51	$180.50	$180.50
Purchase #2	$77.49	11.649%	$86.5168	$86.52	$86.50	$86.50
Purchase #3	$92.34	8.260%	$99.9673	$99.97	$99.95	$100.00
Purchase #4	$85.42	7.510%	$91.835	$91.84	$91.85	$91.80
Purchase #5	$52.68	3.571%	$54.5612	$54.56	$54.55	$54.60
Purchase #6	$235.63	12.632%	$265.3948	$265.39	$265.40	$265.40
Purchase #7	$53.29	12.857%	$60.1415	$60.14	$60.15	$60.10
7 purchase totals =	$763.37		$838.9226	$838.93	$838.90	$838.90