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	$74.30	6.418%	$79.0686	$79.07	$79.05	$79.10
Purchase #2	$166.97	3.106%	$172.1561	$172.16	$172.15	$172.20
Purchase #3	$170.71	7.776%	$183.9844	$183.98	$184.00	$184.00
Purchase #4	$54.35	10.178%	$59.8817	$59.88	$59.90	$59.90
Purchase #5	$100.84	3.185%	$104.0518	$104.05	$104.05	$104.10
Purchase #6	$31.54	12.571%	$35.5049	$35.50	$35.50	$35.50
Purchase #7	$37.31	10.693%	$41.2996	$41.30	$41.30	$41.30
7 purchase totals =	$636.02		$675.9471	$675.94	$675.95	$676.10