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	$12.72	7.844%	$13.7178	$13.72	$13.70	$13.70
Purchase #2	$117.26	13.317%	$132.8755	$132.88	$132.90	$132.90
Purchase #3	$47.31	7.292%	$50.7598	$50.76	$50.75	$50.80
Purchase #4	$174.28	12.732%	$196.4693	$196.47	$196.45	$196.50
Purchase #5	$6.31	8.278%	$6.8323	$6.83	$6.85	$6.80
Purchase #6	$172.93	11.732%	$193.2181	$193.22	$193.20	$193.20
Purchase #7	$96.34	3.235%	$99.4566	$99.46	$99.45	$99.50
7 purchase totals =	$627.15		$693.3294	$693.34	$693.30	$693.40