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	$78.72	6.570%	$83.8919	$83.89	$83.90	$83.90
Purchase #2	$19.74	3.221%	$20.3758	$20.38	$20.40	$20.40
Purchase #3	$46.32	3.594%	$47.9847	$47.98	$48.00	$48.00
Purchase #4	$100.67	3.811%	$104.5065	$104.51	$104.50	$104.50
Purchase #5	$161.35	10.519%	$178.3224	$178.32	$178.30	$178.30
Purchase #6	$224.64	4.653%	$235.0925	$235.09	$235.10	$235.10
Purchase #7	$45.46	4.220%	$47.3784	$47.38	$47.40	$47.40
7 purchase totals =	$676.90		$717.5522	$717.55	$717.60	$717.60