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	$61.28	6.604%	$65.3269	$65.33	$65.35	$65.30
Purchase #2	$21.46	12.839%	$24.2152	$24.22	$24.20	$24.20
Purchase #3	$35.77	5.795%	$37.8429	$37.84	$37.85	$37.80
Purchase #4	$49.72	13.565%	$56.4645	$56.46	$56.45	$56.50
Purchase #5	$189.95	9.565%	$208.1187	$208.12	$208.10	$208.10
Purchase #6	$136.69	4.129%	$142.3339	$142.33	$142.35	$142.30
Purchase #7	$129.55	4.407%	$135.2593	$135.26	$135.25	$135.30
7 purchase totals =	$624.42		$669.5614	$669.56	$669.55	$669.50