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	$40.63	3.529%	$42.0638	$42.06	$42.05	$42.10
Purchase #2	$105.58	7.497%	$113.4953	$113.50	$113.50	$113.50
Purchase #3	$230.45	11.271%	$256.424	$256.42	$256.40	$256.40
Purchase #4	$103.55	12.501%	$116.4948	$116.49	$116.50	$116.50
Purchase #5	$8.71	5.700%	$9.2065	$9.21	$9.20	$9.20
Purchase #6	$80.88	11.469%	$90.1561	$90.16	$90.15	$90.20
Purchase #7	$38.33	5.474%	$40.4282	$40.43	$40.45	$40.40
7 purchase totals =	$608.13		$668.2687	$668.27	$668.25	$668.30