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	$78.42	3.432%	$81.1114	$81.11	$81.10	$81.10
Purchase #2	$221.54	9.430%	$242.4312	$242.43	$242.45	$242.40
Purchase #3	$194.39	13.143%	$219.9387	$219.94	$219.95	$219.90
Purchase #4	$63.25	5.170%	$66.52	$66.52	$66.50	$66.50
Purchase #5	$137.73	11.481%	$153.5428	$153.54	$153.55	$153.50
Purchase #6	$211.77	4.372%	$221.0286	$221.03	$221.05	$221.00
Purchase #7	$148.72	12.838%	$167.8127	$167.81	$167.80	$167.80
7 purchase totals =	$1,055.82		$1,152.3854	$1,152.38	$1,152.40	$1,152.20