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	$100.37	12.817%	$113.2344	$113.23	$113.25	$113.20
Purchase #2	$46.68	13.623%	$53.0392	$53.04	$53.05	$53.00
Purchase #3	$129.45	6.220%	$137.5018	$137.50	$137.50	$137.50
Purchase #4	$80.66	10.445%	$89.0849	$89.08	$89.10	$89.10
Purchase #5	$148.97	5.483%	$157.138	$157.14	$157.15	$157.10
Purchase #6	$34.39	11.632%	$38.3902	$38.39	$38.40	$38.40
Purchase #7	$73.81	12.679%	$83.1684	$83.17	$83.15	$83.20
7 purchase totals =	$614.33		$671.5569	$671.55	$671.60	$671.50