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	$144.54	5.118%	$151.9376	$151.94	$151.95	$151.90
Purchase #2	$193.58	4.793%	$202.8583	$202.86	$202.85	$202.90
Purchase #3	$89.97	5.647%	$95.0506	$95.05	$95.05	$95.10
Purchase #4	$80.65	3.264%	$83.2824	$83.28	$83.30	$83.30
Purchase #5	$97.45	3.223%	$100.5908	$100.59	$100.60	$100.60
Purchase #6	$223.59	8.817%	$243.3039	$243.30	$243.30	$243.30
Purchase #7	$101.49	11.840%	$113.5064	$113.51	$113.50	$113.50
7 purchase totals =	$931.27		$990.5300	$990.53	$990.55	$990.60