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	$99.55	6.379%	$105.9003	$105.90	$105.90	$105.90
Purchase #2	$185.96	5.286%	$195.7898	$195.79	$195.80	$195.80
Purchase #3	$47.94	10.674%	$53.0571	$53.06	$53.05	$53.10
Purchase #4	$37.72	12.124%	$42.2932	$42.29	$42.30	$42.30
Purchase #5	$175.48	6.791%	$187.3968	$187.40	$187.40	$187.40
Purchase #6	$243.79	6.138%	$258.7538	$258.75	$258.75	$258.80
Purchase #7	$158.72	10.173%	$174.8666	$174.87	$174.85	$174.90
7 purchase totals =	$949.16		$1,018.0576	$1,018.06	$1,018.05	$1,018.20