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	$29.37	13.346%	$33.2897	$33.29	$33.30	$33.30
Purchase #2	$95.93	13.851%	$109.2173	$109.22	$109.20	$109.20
Purchase #3	$42.86	13.669%	$48.7185	$48.72	$48.70	$48.70
Purchase #4	$92.96	13.456%	$105.4687	$105.47	$105.45	$105.50
Purchase #5	$36.33	4.704%	$38.039	$38.04	$38.05	$38.00
Purchase #6	$111.34	13.570%	$126.4488	$126.45	$126.45	$126.40
Purchase #7	$142.92	12.347%	$160.5663	$160.57	$160.55	$160.60
7 purchase totals =	$551.71		$621.7483	$621.76	$621.70	$621.70