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	$138.46	8.858%	$150.7248	$150.72	$150.70	$150.70
Purchase #2	$42.35	3.667%	$43.903	$43.90	$43.90	$43.90
Purchase #3	$165.27	5.190%	$173.8475	$173.85	$173.85	$173.80
Purchase #4	$167.58	10.562%	$185.2798	$185.28	$185.30	$185.30
Purchase #5	$124.46	6.245%	$132.2325	$132.23	$132.25	$132.20
Purchase #6	$204.35	5.222%	$215.0212	$215.02	$215.00	$215.00
Purchase #7	$20.58	4.459%	$21.4977	$21.50	$21.50	$21.50
7 purchase totals =	$863.05		$922.5065	$922.50	$922.50	$922.40