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	$189.78	5.685%	$200.569	$200.57	$200.55	$200.60
Purchase #2	$132.25	6.809%	$141.2549	$141.25	$141.25	$141.30
Purchase #3	$72.74	10.735%	$80.5486	$80.55	$80.55	$80.50
Purchase #4	$244.77	12.733%	$275.9366	$275.94	$275.95	$275.90
Purchase #5	$89.45	11.121%	$99.3977	$99.40	$99.40	$99.40
Purchase #6	$203.88	6.347%	$216.8203	$216.82	$216.80	$216.80
Purchase #7	$136.51	5.762%	$144.3757	$144.38	$144.40	$144.40
7 purchase totals =	$1,069.38		$1,158.9028	$1,158.91	$1,158.90	$1,158.90