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	$105.58	5.418%	$111.3003	$111.30	$111.30	$111.30
Purchase #2	$206.36	4.568%	$215.7865	$215.79	$215.80	$215.80
Purchase #3	$26.61	5.478%	$28.0677	$28.07	$28.05	$28.10
Purchase #4	$144.67	3.530%	$149.7769	$149.78	$149.80	$149.80
Purchase #5	$45.40	5.514%	$47.9034	$47.90	$47.90	$47.90
Purchase #6	$48.69	9.661%	$53.3939	$53.39	$53.40	$53.40
Purchase #7	$222.45	12.482%	$250.2162	$250.22	$250.20	$250.20
7 purchase totals =	$799.76		$856.4449	$856.45	$856.45	$856.50