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	$104.73	7.309%	$112.3847	$112.38	$112.40	$112.40
Purchase #2	$49.42	9.300%	$54.0161	$54.02	$54.00	$54.00
Purchase #3	$115.39	13.751%	$131.2573	$131.26	$131.25	$131.30
Purchase #4	$96.53	10.190%	$106.3664	$106.37	$106.35	$106.40
Purchase #5	$65.35	11.129%	$72.6228	$72.62	$72.60	$72.60
Purchase #6	$57.73	4.528%	$60.344	$60.34	$60.35	$60.30
Purchase #7	$121.74	8.257%	$131.7921	$131.79	$131.80	$131.80
7 purchase totals =	$610.89		$668.7834	$668.78	$668.75	$668.80