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	$59.57	12.537%	$67.0383	$67.04	$67.05	$67.00
Purchase #2	$146.92	3.202%	$151.6244	$151.62	$151.60	$151.60
Purchase #3	$173.87	6.588%	$185.3246	$185.32	$185.30	$185.30
Purchase #4	$7.60	5.796%	$8.0405	$8.04	$8.05	$8.00
Purchase #5	$76.79	4.641%	$80.3538	$80.35	$80.35	$80.40
Purchase #6	$145.34	13.300%	$164.6702	$164.67	$164.65	$164.70
Purchase #7	$189.26	4.695%	$198.1458	$198.15	$198.15	$198.10
7 purchase totals =	$799.35		$855.1976	$855.19	$855.15	$855.10