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	$51.89	4.626%	$54.2904	$54.29	$54.30	$54.30
Purchase #2	$55.51	6.330%	$59.0238	$59.02	$59.00	$59.00
Purchase #3	$18.81	13.188%	$21.2907	$21.29	$21.30	$21.30
Purchase #4	$5.40	12.420%	$6.0707	$6.07	$6.05	$6.10
Purchase #5	$27.98	9.194%	$30.5525	$30.55	$30.55	$30.60
Purchase #6	$248.85	10.611%	$275.2555	$275.26	$275.25	$275.30
Purchase #7	$219.65	5.767%	$232.3172	$232.32	$232.30	$232.30
7 purchase totals =	$628.09		$678.8008	$678.80	$678.75	$678.90