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	$53.69	8.696%	$58.3589	$58.36	$58.35	$58.40
Purchase #2	$87.89	5.578%	$92.7925	$92.79	$92.80	$92.80
Purchase #3	$38.85	10.585%	$42.9623	$42.96	$42.95	$43.00
Purchase #4	$56.44	3.665%	$58.5085	$58.51	$58.50	$58.50
Purchase #5	$201.40	10.187%	$221.9166	$221.92	$221.90	$221.90
Purchase #6	$40.53	12.664%	$45.6627	$45.66	$45.65	$45.70
Purchase #7	$111.38	4.570%	$116.4701	$116.47	$116.45	$116.50
7 purchase totals =	$590.18		$636.6716	$636.67	$636.60	$636.80