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	$83.34	6.609%	$88.8479	$88.85	$88.85	$88.80
Purchase #2	$137.81	3.785%	$143.0261	$143.03	$143.05	$143.00
Purchase #3	$37.82	11.257%	$42.0774	$42.08	$42.10	$42.10
Purchase #4	$137.65	8.646%	$149.5512	$149.55	$149.55	$149.60
Purchase #5	$17.27	5.284%	$18.1825	$18.18	$18.20	$18.20
Purchase #6	$162.67	7.779%	$175.3241	$175.32	$175.30	$175.30
Purchase #7	$128.30	4.685%	$134.3109	$134.31	$134.30	$134.30
7 purchase totals =	$704.86		$751.3201	$751.32	$751.35	$751.30