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	$116.52	12.824%	$131.4625	$131.46	$131.45	$131.50
Purchase #2	$51.88	7.226%	$55.6288	$55.63	$55.65	$55.60
Purchase #3	$70.39	10.871%	$78.0421	$78.04	$78.05	$78.00
Purchase #4	$131.88	7.342%	$141.5626	$141.56	$141.55	$141.60
Purchase #5	$58.33	6.140%	$61.9115	$61.91	$61.90	$61.90
Purchase #6	$230.65	11.759%	$257.7721	$257.77	$257.75	$257.80
Purchase #7	$40.26	3.797%	$41.7887	$41.79	$41.80	$41.80
7 purchase totals =	$699.91		$768.1683	$768.16	$768.15	$768.20