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	$160.78	8.777%	$174.8917	$174.89	$174.90	$174.90
Purchase #2	$184.78	7.467%	$198.5775	$198.58	$198.60	$198.60
Purchase #3	$5.72	8.617%	$6.2129	$6.21	$6.20	$6.20
Purchase #4	$10.80	10.290%	$11.9113	$11.91	$11.90	$11.90
Purchase #5	$85.40	5.788%	$90.343	$90.34	$90.35	$90.30
Purchase #6	$242.65	3.329%	$250.7278	$250.73	$250.75	$250.70
Purchase #7	$101.71	9.140%	$111.0063	$111.01	$111.00	$111.00
7 purchase totals =	$791.84		$843.6705	$843.67	$843.70	$843.60