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	$102.78	13.283%	$116.4323	$116.43	$116.45	$116.40
Purchase #2	$77.90	6.777%	$83.1793	$83.18	$83.20	$83.20
Purchase #3	$114.28	7.170%	$122.4739	$122.47	$122.45	$122.50
Purchase #4	$171.84	9.449%	$188.0772	$188.08	$188.10	$188.10
Purchase #5	$218.53	4.782%	$228.9801	$228.98	$229.00	$229.00
Purchase #6	$196.29	13.425%	$222.6419	$222.64	$222.65	$222.60
Purchase #7	$98.52	6.626%	$105.0479	$105.05	$105.05	$105.00
7 purchase totals =	$980.14		$1,066.8326	$1,066.83	$1,066.90	$1,066.80