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	$197.37	3.262%	$203.8082	$203.81	$203.80	$203.80
Purchase #2	$164.41	11.529%	$183.3648	$183.36	$183.35	$183.40
Purchase #3	$132.31	6.808%	$141.3177	$141.32	$141.30	$141.30
Purchase #4	$164.94	4.570%	$172.4778	$172.48	$172.50	$172.50
Purchase #5	$146.40	11.704%	$163.5347	$163.53	$163.55	$163.50
Purchase #6	$225.50	13.355%	$255.6155	$255.62	$255.60	$255.60
Purchase #7	$54.46	8.584%	$59.1348	$59.13	$59.15	$59.10
7 purchase totals =	$1,085.39		$1,179.2535	$1,179.25	$1,179.25	$1,179.20