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	$100.62	8.788%	$109.4625	$109.46	$109.45	$109.50
Purchase #2	$237.52	11.298%	$264.355	$264.36	$264.35	$264.40
Purchase #3	$247.89	12.858%	$279.7637	$279.76	$279.75	$279.80
Purchase #4	$67.86	8.680%	$73.7502	$73.75	$73.75	$73.80
Purchase #5	$64.41	11.425%	$71.7688	$71.77	$71.75	$71.80
Purchase #6	$173.99	10.452%	$192.1754	$192.18	$192.20	$192.20
Purchase #7	$127.31	3.167%	$131.3419	$131.34	$131.35	$131.30
7 purchase totals =	$1,019.60		$1,122.6175	$1,122.62	$1,122.60	$1,122.80