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	$118.53	6.405%	$126.1218	$126.12	$126.10	$126.10
Purchase #2	$148.46	13.480%	$168.4724	$168.47	$168.45	$168.50
Purchase #3	$144.53	6.239%	$153.5472	$153.55	$153.55	$153.50
Purchase #4	$140.28	10.327%	$154.7667	$154.77	$154.75	$154.80
Purchase #5	$70.38	12.311%	$79.0445	$79.04	$79.05	$79.00
Purchase #6	$39.95	5.589%	$42.1828	$42.18	$42.20	$42.20
Purchase #7	$130.65	6.522%	$139.171	$139.17	$139.15	$139.20
7 purchase totals =	$792.78		$863.3064	$863.30	$863.25	$863.30