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	$73.57	7.158%	$78.8361	$78.84	$78.85	$78.80
Purchase #2	$133.52	13.537%	$151.5946	$151.59	$151.60	$151.60
Purchase #3	$94.89	8.662%	$103.1094	$103.11	$103.10	$103.10
Purchase #4	$92.46	5.124%	$97.1977	$97.20	$97.20	$97.20
Purchase #5	$229.60	12.596%	$258.5204	$258.52	$258.50	$258.50
Purchase #6	$34.48	6.388%	$36.6826	$36.68	$36.70	$36.70
Purchase #7	$91.45	4.226%	$95.3147	$95.31	$95.30	$95.30
7 purchase totals =	$749.97		$821.2555	$821.25	$821.25	$821.20