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	$52.82	9.868%	$58.0323	$58.03	$58.05	$58.00
Purchase #2	$65.48	12.776%	$73.8457	$73.85	$73.85	$73.80
Purchase #3	$26.27	7.584%	$28.2623	$28.26	$28.25	$28.30
Purchase #4	$131.40	10.429%	$145.1037	$145.10	$145.10	$145.10
Purchase #5	$178.56	3.780%	$185.3096	$185.31	$185.30	$185.30
Purchase #6	$61.93	5.277%	$65.198	$65.20	$65.20	$65.20
Purchase #7	$104.88	6.328%	$111.5168	$111.52	$111.50	$111.50
7 purchase totals =	$621.34		$667.2684	$667.27	$667.25	$667.20