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	$93.30	6.363%	$99.2367	$99.24	$99.25	$99.20
Purchase #2	$167.63	10.538%	$185.2948	$185.29	$185.30	$185.30
Purchase #3	$95.80	10.591%	$105.9462	$105.95	$105.95	$105.90
Purchase #4	$5.78	8.368%	$6.2637	$6.26	$6.25	$6.30
Purchase #5	$104.30	13.407%	$118.2835	$118.28	$118.30	$118.30
Purchase #6	$207.63	13.349%	$235.3465	$235.35	$235.35	$235.30
Purchase #7	$216.63	5.182%	$227.8558	$227.86	$227.85	$227.90
7 purchase totals =	$891.07		$978.2272	$978.23	$978.25	$978.20