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	$204.74	3.489%	$211.8834	$211.88	$211.90	$211.90
Purchase #2	$183.88	3.636%	$190.5659	$190.57	$190.55	$190.60
Purchase #3	$32.51	8.577%	$35.2984	$35.30	$35.30	$35.30
Purchase #4	$190.27	10.574%	$210.3891	$210.39	$210.40	$210.40
Purchase #5	$16.86	6.784%	$18.0038	$18.00	$18.00	$18.00
Purchase #6	$11.73	9.295%	$12.8203	$12.82	$12.80	$12.80
Purchase #7	$88.58	13.360%	$100.4143	$100.41	$100.40	$100.40
7 purchase totals =	$728.57		$779.3752	$779.37	$779.35	$779.40