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	$65.40	4.296%	$68.2096	$68.21	$68.20	$68.20
Purchase #2	$20.89	13.538%	$23.7181	$23.72	$23.70	$23.70
Purchase #3	$81.98	7.872%	$88.4335	$88.43	$88.45	$88.40
Purchase #4	$29.91	4.619%	$31.2915	$31.29	$31.30	$31.30
Purchase #5	$85.85	6.283%	$91.244	$91.24	$91.25	$91.20
Purchase #6	$145.78	3.211%	$150.461	$150.46	$150.45	$150.50
Purchase #7	$80.27	7.726%	$86.4717	$86.47	$86.45	$86.50
7 purchase totals =	$510.08		$539.8294	$539.82	$539.80	$539.80