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	$90.38	6.409%	$96.1725	$96.17	$96.15	$96.20
Purchase #2	$169.82	6.410%	$180.7055	$180.71	$180.70	$180.70
Purchase #3	$159.42	10.627%	$176.3616	$176.36	$176.35	$176.40
Purchase #4	$61.42	9.123%	$67.0233	$67.02	$67.00	$67.00
Purchase #5	$222.33	3.205%	$229.4557	$229.46	$229.45	$229.50
Purchase #6	$120.94	9.563%	$132.5055	$132.51	$132.50	$132.50
Purchase #7	$43.89	12.196%	$49.2428	$49.24	$49.25	$49.20
7 purchase totals =	$868.20		$931.4669	$931.47	$931.40	$931.50