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	$96.52	13.772%	$109.8127	$109.81	$109.80	$109.80
Purchase #2	$127.78	9.195%	$139.5294	$139.53	$139.55	$139.50
Purchase #3	$149.39	12.540%	$168.1235	$168.12	$168.10	$168.10
Purchase #4	$179.64	10.799%	$199.0393	$199.04	$199.05	$199.00
Purchase #5	$50.71	3.750%	$52.6116	$52.61	$52.60	$52.60
Purchase #6	$233.81	10.708%	$258.8464	$258.85	$258.85	$258.80
Purchase #7	$172.79	10.710%	$191.2958	$191.30	$191.30	$191.30
7 purchase totals =	$1,010.64		$1,119.2587	$1,119.26	$1,119.25	$1,119.10