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	$55.77	6.861%	$59.5964	$59.60	$59.60	$59.60
Purchase #2	$99.40	12.373%	$111.6988	$111.70	$111.70	$111.70
Purchase #3	$38.45	8.361%	$41.6648	$41.66	$41.65	$41.70
Purchase #4	$94.57	8.421%	$102.5337	$102.53	$102.55	$102.50
Purchase #5	$232.81	5.140%	$244.7764	$244.78	$244.80	$244.80
Purchase #6	$77.72	9.745%	$85.2938	$85.29	$85.30	$85.30
Purchase #7	$214.67	3.258%	$221.6639	$221.66	$221.65	$221.70
7 purchase totals =	$813.39		$867.2278	$867.22	$867.25	$867.30