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	$218.93	9.851%	$240.4968	$240.50	$240.50	$240.50
Purchase #2	$221.55	10.249%	$244.2567	$244.26	$244.25	$244.30
Purchase #3	$91.67	9.763%	$100.6197	$100.62	$100.60	$100.60
Purchase #4	$190.96	10.384%	$210.7893	$210.79	$210.80	$210.80
Purchase #5	$162.72	3.621%	$168.6121	$168.61	$168.60	$168.60
Purchase #6	$45.96	4.834%	$48.1817	$48.18	$48.20	$48.20
Purchase #7	$122.99	9.374%	$134.5191	$134.52	$134.50	$134.50
7 purchase totals =	$1,054.78		$1,147.4754	$1,147.48	$1,147.45	$1,147.50