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	$37.27	13.433%	$42.2765	$42.28	$42.30	$42.30
Purchase #2	$84.70	11.515%	$94.4532	$94.45	$94.45	$94.50
Purchase #3	$189.82	13.472%	$215.3926	$215.39	$215.40	$215.40
Purchase #4	$11.40	3.191%	$11.7638	$11.76	$11.75	$11.80
Purchase #5	$166.66	13.381%	$188.9608	$188.96	$188.95	$189.00
Purchase #6	$161.36	3.395%	$166.8382	$166.84	$166.85	$166.80
Purchase #7	$201.25	10.525%	$222.4316	$222.43	$222.45	$222.40
7 purchase totals =	$852.46		$942.1167	$942.11	$942.15	$942.20