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	$52.33	5.635%	$55.2788	$55.28	$55.30	$55.30
Purchase #2	$136.69	10.463%	$150.9919	$150.99	$151.00	$151.00
Purchase #3	$93.88	4.243%	$97.8633	$97.86	$97.85	$97.90
Purchase #4	$139.43	5.726%	$147.4138	$147.41	$147.40	$147.40
Purchase #5	$99.42	4.833%	$104.225	$104.23	$104.25	$104.20
Purchase #6	$16.54	4.335%	$17.257	$17.26	$17.25	$17.30
Purchase #7	$6.96	6.705%	$7.4267	$7.43	$7.45	$7.40
7 purchase totals =	$545.25		$580.4565	$580.46	$580.50	$580.50