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	$50.66	13.635%	$57.5675	$57.57	$57.55	$57.60
Purchase #2	$54.29	11.264%	$60.4052	$60.41	$60.40	$60.40
Purchase #3	$104.91	4.195%	$109.311	$109.31	$109.30	$109.30
Purchase #4	$47.77	12.403%	$53.6949	$53.69	$53.70	$53.70
Purchase #5	$5.98	7.173%	$6.4089	$6.41	$6.40	$6.40
Purchase #6	$122.52	4.412%	$127.9256	$127.93	$127.95	$127.90
Purchase #7	$74.58	7.640%	$80.2779	$80.28	$80.30	$80.30
7 purchase totals =	$460.71		$495.5910	$495.60	$495.60	$495.60