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	$202.52	8.755%	$220.2506	$220.25	$220.25	$220.30
Purchase #2	$46.32	12.438%	$52.0813	$52.08	$52.10	$52.10
Purchase #3	$159.70	6.421%	$169.9543	$169.95	$169.95	$170.00
Purchase #4	$59.76	4.322%	$62.3428	$62.34	$62.35	$62.30
Purchase #5	$33.65	10.803%	$37.2852	$37.29	$37.30	$37.30
Purchase #6	$95.71	3.590%	$99.146	$99.15	$99.15	$99.10
Purchase #7	$159.87	13.324%	$181.1711	$181.17	$181.15	$181.20
7 purchase totals =	$757.53		$822.2313	$822.23	$822.25	$822.30