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	$99.59	6.514%	$106.0773	$106.08	$106.10	$106.10
Purchase #2	$95.72	4.695%	$100.2141	$100.21	$100.20	$100.20
Purchase #3	$203.40	6.807%	$217.2454	$217.25	$217.25	$217.20
Purchase #4	$102.59	8.674%	$111.4887	$111.49	$111.50	$111.50
Purchase #5	$100.96	13.596%	$114.6865	$114.69	$114.70	$114.70
Purchase #6	$84.68	7.698%	$91.1987	$91.20	$91.20	$91.20
Purchase #7	$174.90	3.666%	$181.3118	$181.31	$181.30	$181.30
7 purchase totals =	$861.84		$922.2225	$922.23	$922.25	$922.20