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	$49.45	9.820%	$54.306	$54.31	$54.30	$54.30
Purchase #2	$187.82	10.111%	$206.8105	$206.81	$206.80	$206.80
Purchase #3	$18.60	5.582%	$19.6383	$19.64	$19.65	$19.60
Purchase #4	$248.88	12.800%	$280.7366	$280.74	$280.75	$280.70
Purchase #5	$51.76	11.133%	$57.5224	$57.52	$57.50	$57.50
Purchase #6	$95.26	7.562%	$102.4636	$102.46	$102.45	$102.50
Purchase #7	$152.40	13.191%	$172.5031	$172.50	$172.50	$172.50
7 purchase totals =	$804.17		$893.9805	$893.98	$893.95	$893.90