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	$250.70	8.252%	$271.3878	$271.39	$271.40	$271.40
Purchase #2	$165.29	4.264%	$172.338	$172.34	$172.35	$172.30
Purchase #3	$154.59	9.331%	$169.0148	$169.01	$169.00	$169.00
Purchase #4	$30.91	3.549%	$32.007	$32.01	$32.00	$32.00
Purchase #5	$113.64	11.665%	$126.8961	$126.90	$126.90	$126.90
Purchase #6	$121.49	5.252%	$127.8707	$127.87	$127.85	$127.90
Purchase #7	$124.61	5.247%	$131.1483	$131.15	$131.15	$131.10
7 purchase totals =	$961.23		$1,030.6627	$1,030.67	$1,030.65	$1,030.60