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	$169.55	11.662%	$189.3229	$189.32	$189.30	$189.30
Purchase #2	$81.92	4.391%	$85.5171	$85.52	$85.50	$85.50
Purchase #3	$59.52	13.485%	$67.5463	$67.55	$67.55	$67.50
Purchase #4	$153.43	3.600%	$158.9535	$158.95	$158.95	$159.00
Purchase #5	$8.82	6.227%	$9.3692	$9.37	$9.35	$9.40
Purchase #6	$84.42	4.133%	$87.9091	$87.91	$87.90	$87.90
Purchase #7	$101.34	9.667%	$111.1365	$111.14	$111.15	$111.10
7 purchase totals =	$659.00		$709.7546	$709.76	$709.70	$709.70