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	$81.30	6.131%	$86.2845	$86.28	$86.30	$86.30
Purchase #2	$58.71	12.171%	$65.8556	$65.86	$65.85	$65.90
Purchase #3	$66.57	7.436%	$71.5201	$71.52	$71.50	$71.50
Purchase #4	$141.64	12.340%	$159.1184	$159.12	$159.10	$159.10
Purchase #5	$139.30	9.507%	$152.5433	$152.54	$152.55	$152.50
Purchase #6	$139.77	4.546%	$146.1239	$146.12	$146.10	$146.10
Purchase #7	$33.78	5.692%	$35.7028	$35.70	$35.70	$35.70
7 purchase totals =	$661.07		$717.1486	$717.14	$717.10	$717.10