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	$18.51	8.799%	$20.1387	$20.14	$20.15	$20.10
Purchase #2	$79.56	12.272%	$89.3236	$89.32	$89.30	$89.30
Purchase #3	$14.25	3.748%	$14.7841	$14.78	$14.80	$14.80
Purchase #4	$113.97	11.245%	$126.7859	$126.79	$126.80	$126.80
Purchase #5	$116.72	7.796%	$125.8195	$125.82	$125.80	$125.80
Purchase #6	$209.35	6.814%	$223.6151	$223.62	$223.60	$223.60
Purchase #7	$107.46	4.451%	$112.243	$112.24	$112.25	$112.20
7 purchase totals =	$659.82		$712.7099	$712.71	$712.70	$712.60