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	$121.98	8.117%	$131.8811	$131.88	$131.90	$131.90
Purchase #2	$86.99	6.172%	$92.359	$92.36	$92.35	$92.40
Purchase #3	$121.44	4.635%	$127.0687	$127.07	$127.05	$127.10
Purchase #4	$53.89	3.527%	$55.7907	$55.79	$55.80	$55.80
Purchase #5	$80.86	5.609%	$85.3954	$85.40	$85.40	$85.40
Purchase #6	$101.28	11.683%	$113.1125	$113.11	$113.10	$113.10
Purchase #7	$249.45	11.452%	$278.017	$278.02	$278.00	$278.00
7 purchase totals =	$815.89		$883.6244	$883.63	$883.60	$883.70