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	$220.25	4.234%	$229.5754	$229.58	$229.60	$229.60
Purchase #2	$158.97	5.254%	$167.3223	$167.32	$167.30	$167.30
Purchase #3	$194.58	5.649%	$205.5718	$205.57	$205.55	$205.60
Purchase #4	$132.42	8.166%	$143.2334	$143.23	$143.25	$143.20
Purchase #5	$250.35	5.808%	$264.8903	$264.89	$264.90	$264.90
Purchase #6	$233.79	6.766%	$249.6082	$249.61	$249.60	$249.60
Purchase #7	$159.44	3.860%	$165.5944	$165.59	$165.60	$165.60
7 purchase totals =	$1,349.80		$1,425.7958	$1,425.79	$1,425.80	$1,425.80