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	$123.45	8.643%	$134.1198	$134.12	$134.10	$134.10
Purchase #2	$40.71	13.521%	$46.2144	$46.21	$46.20	$46.20
Purchase #3	$75.27	6.780%	$80.3733	$80.37	$80.35	$80.40
Purchase #4	$91.49	7.562%	$98.4085	$98.41	$98.40	$98.40
Purchase #5	$132.60	7.741%	$142.8646	$142.86	$142.85	$142.90
Purchase #6	$170.52	11.725%	$190.5135	$190.51	$190.50	$190.50
Purchase #7	$129.33	9.582%	$141.7224	$141.72	$141.70	$141.70
7 purchase totals =	$763.37		$834.2165	$834.20	$834.10	$834.20