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	$87.25	4.657%	$91.3132	$91.31	$91.30	$91.30
Purchase #2	$150.64	5.421%	$158.8062	$158.81	$158.80	$158.80
Purchase #3	$123.60	4.651%	$129.3486	$129.35	$129.35	$129.30
Purchase #4	$225.51	8.437%	$244.5363	$244.54	$244.55	$244.50
Purchase #5	$6.86	13.314%	$7.7733	$7.77	$7.75	$7.80
Purchase #6	$111.50	13.478%	$126.528	$126.53	$126.55	$126.50
Purchase #7	$46.36	12.672%	$52.2347	$52.23	$52.25	$52.20
7 purchase totals =	$751.72		$810.5403	$810.54	$810.55	$810.40