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	$65.85	6.833%	$70.3495	$70.35	$70.35	$70.30
Purchase #2	$237.73	12.226%	$266.7949	$266.79	$266.80	$266.80
Purchase #3	$92.80	8.107%	$100.3233	$100.32	$100.30	$100.30
Purchase #4	$250.52	8.215%	$271.1002	$271.10	$271.10	$271.10
Purchase #5	$127.47	6.746%	$136.0691	$136.07	$136.05	$136.10
Purchase #6	$123.49	5.735%	$130.5722	$130.57	$130.55	$130.60
Purchase #7	$144.96	7.749%	$156.193	$156.19	$156.20	$156.20
7 purchase totals =	$1,042.82		$1,131.4022	$1,131.39	$1,131.35	$1,131.40