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	$179.80	3.205%	$185.5626	$185.56	$185.55	$185.60
Purchase #2	$42.81	7.234%	$45.9069	$45.91	$45.90	$45.90
Purchase #3	$201.74	13.716%	$229.4107	$229.41	$229.40	$229.40
Purchase #4	$97.80	5.731%	$103.4049	$103.40	$103.40	$103.40
Purchase #5	$239.68	9.460%	$262.3537	$262.35	$262.35	$262.40
Purchase #6	$38.90	4.468%	$40.6381	$40.64	$40.65	$40.60
Purchase #7	$246.40	3.335%	$254.6174	$254.62	$254.60	$254.60
7 purchase totals =	$1,047.13		$1,121.8943	$1,121.89	$1,121.85	$1,121.90