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	$6.83	5.785%	$7.2251	$7.23	$7.25	$7.20
Purchase #2	$106.86	11.266%	$118.8988	$118.90	$118.90	$118.90
Purchase #3	$12.33	3.333%	$12.741	$12.74	$12.75	$12.70
Purchase #4	$138.77	4.795%	$145.424	$145.42	$145.40	$145.40
Purchase #5	$89.89	12.632%	$101.2449	$101.24	$101.25	$101.20
Purchase #6	$143.47	8.766%	$156.0466	$156.05	$156.05	$156.00
Purchase #7	$139.43	4.300%	$145.4255	$145.43	$145.45	$145.40
7 purchase totals =	$637.58		$687.0059	$687.01	$687.05	$686.80