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	$52.72	13.384%	$59.776	$59.78	$59.80	$59.80
Purchase #2	$189.72	10.754%	$210.1225	$210.12	$210.10	$210.10
Purchase #3	$106.62	5.308%	$112.2794	$112.28	$112.30	$112.30
Purchase #4	$27.91	7.154%	$29.9067	$29.91	$29.90	$29.90
Purchase #5	$156.94	8.433%	$170.1748	$170.17	$170.15	$170.20
Purchase #6	$179.63	5.410%	$189.348	$189.35	$189.35	$189.30
Purchase #7	$58.77	5.228%	$61.8425	$61.84	$61.85	$61.80
7 purchase totals =	$772.31		$833.4499	$833.45	$833.45	$833.40