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	$212.74	13.805%	$242.1088	$242.11	$242.10	$242.10
Purchase #2	$29.70	6.785%	$31.7151	$31.72	$31.70	$31.70
Purchase #3	$30.31	11.861%	$33.9051	$33.91	$33.90	$33.90
Purchase #4	$231.76	9.514%	$253.8096	$253.81	$253.80	$253.80
Purchase #5	$172.90	7.102%	$185.1794	$185.18	$185.20	$185.20
Purchase #6	$205.60	8.591%	$223.2631	$223.26	$223.25	$223.30
Purchase #7	$132.25	5.401%	$139.3928	$139.39	$139.40	$139.40
7 purchase totals =	$1,015.26		$1,109.3739	$1,109.38	$1,109.35	$1,109.40