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	$69.57	13.369%	$78.8708	$78.87	$78.85	$78.90
Purchase #2	$181.42	4.482%	$189.5512	$189.55	$189.55	$189.60
Purchase #3	$58.62	11.300%	$65.2441	$65.24	$65.25	$65.20
Purchase #4	$69.86	10.226%	$77.0039	$77.00	$77.00	$77.00
Purchase #5	$81.37	5.223%	$85.62	$85.62	$85.60	$85.60
Purchase #6	$172.86	9.636%	$189.5168	$189.52	$189.50	$189.50
Purchase #7	$226.98	3.326%	$234.5294	$234.53	$234.55	$234.50
7 purchase totals =	$860.68		$920.3362	$920.33	$920.30	$920.30