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	$20.39	6.447%	$21.7045	$21.70	$21.70	$21.70
Purchase #2	$139.83	6.653%	$149.1329	$149.13	$149.15	$149.10
Purchase #3	$72.62	6.659%	$77.4558	$77.46	$77.45	$77.50
Purchase #4	$189.60	3.760%	$196.729	$196.73	$196.75	$196.70
Purchase #5	$34.90	12.154%	$39.1417	$39.14	$39.15	$39.10
Purchase #6	$173.38	4.116%	$180.5163	$180.52	$180.50	$180.50
Purchase #7	$36.48	4.755%	$38.2146	$38.21	$38.20	$38.20
7 purchase totals =	$667.20		$702.8948	$702.89	$702.90	$702.80