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	$172.77	10.261%	$190.4979	$190.50	$190.50	$190.50
Purchase #2	$159.91	6.262%	$169.9236	$169.92	$169.90	$169.90
Purchase #3	$242.29	6.329%	$257.6245	$257.62	$257.60	$257.60
Purchase #4	$249.48	12.361%	$280.3182	$280.32	$280.30	$280.30
Purchase #5	$41.81	8.471%	$45.3517	$45.35	$45.35	$45.40
Purchase #6	$89.58	3.455%	$92.675	$92.68	$92.70	$92.70
Purchase #7	$167.94	12.792%	$189.4229	$189.42	$189.40	$189.40
7 purchase totals =	$1,123.78		$1,225.8138	$1,225.81	$1,225.75	$1,225.80