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	$12.34	3.752%	$12.803	$12.80	$12.80	$12.80
Purchase #2	$121.63	13.261%	$137.7594	$137.76	$137.75	$137.80
Purchase #3	$216.26	4.462%	$225.9095	$225.91	$225.90	$225.90
Purchase #4	$173.76	10.262%	$191.5913	$191.59	$191.60	$191.60
Purchase #5	$245.80	3.157%	$253.5599	$253.56	$253.55	$253.60
Purchase #6	$204.32	10.411%	$225.5918	$225.59	$225.60	$225.60
Purchase #7	$86.32	3.142%	$89.0322	$89.03	$89.05	$89.00
7 purchase totals =	$1,060.43		$1,136.2471	$1,136.24	$1,136.25	$1,136.30