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	$248.96	12.536%	$280.1696	$280.17	$280.15	$280.20
Purchase #2	$106.42	6.433%	$113.266	$113.27	$113.25	$113.30
Purchase #3	$172.67	3.478%	$178.6755	$178.68	$178.70	$178.70
Purchase #4	$192.92	3.700%	$200.058	$200.06	$200.05	$200.10
Purchase #5	$106.44	3.805%	$110.49	$110.49	$110.50	$110.50
Purchase #6	$65.58	8.459%	$71.1274	$71.13	$71.15	$71.10
Purchase #7	$53.65	4.490%	$56.0589	$56.06	$56.05	$56.10
7 purchase totals =	$946.64		$1,009.8454	$1,009.86	$1,009.85	$1,010.00