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	$161.96	3.837%	$168.1744	$168.17	$168.15	$168.20
Purchase #2	$213.97	8.227%	$231.5733	$231.57	$231.55	$231.60
Purchase #3	$42.33	6.435%	$45.0539	$45.05	$45.05	$45.10
Purchase #4	$174.66	10.177%	$192.4351	$192.44	$192.45	$192.40
Purchase #5	$47.29	13.283%	$53.5715	$53.57	$53.55	$53.60
Purchase #6	$91.43	4.229%	$95.2966	$95.30	$95.30	$95.30
Purchase #7	$128.25	3.196%	$132.3489	$132.35	$132.35	$132.30
7 purchase totals =	$859.89		$918.4537	$918.45	$918.40	$918.50