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	$116.72	3.182%	$120.434	$120.43	$120.45	$120.40
Purchase #2	$135.34	6.506%	$144.1452	$144.15	$144.15	$144.10
Purchase #3	$129.53	13.383%	$146.865	$146.87	$146.85	$146.90
Purchase #4	$101.30	12.173%	$113.6312	$113.63	$113.65	$113.60
Purchase #5	$94.29	11.317%	$104.9608	$104.96	$104.95	$105.00
Purchase #6	$74.73	4.411%	$78.0263	$78.03	$78.05	$78.00
Purchase #7	$70.68	10.268%	$77.9374	$77.94	$77.95	$77.90
7 purchase totals =	$722.59		$785.9999	$786.01	$786.05	$785.90