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	$63.45	13.120%	$71.7746	$71.77	$71.75	$71.80
Purchase #2	$223.58	7.466%	$240.2725	$240.27	$240.25	$240.30
Purchase #3	$67.28	5.572%	$71.0288	$71.03	$71.05	$71.00
Purchase #4	$171.84	6.493%	$182.9976	$183.00	$183.00	$183.00
Purchase #5	$172.99	13.420%	$196.2053	$196.21	$196.20	$196.20
Purchase #6	$40.35	4.657%	$42.2291	$42.23	$42.25	$42.20
Purchase #7	$188.68	5.341%	$198.7574	$198.76	$198.75	$198.80
7 purchase totals =	$928.17		$1,003.2653	$1,003.27	$1,003.25	$1,003.30