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	$20.86	3.438%	$21.5772	$21.58	$21.60	$21.60
Purchase #2	$98.61	4.723%	$103.2674	$103.27	$103.25	$103.30
Purchase #3	$226.64	12.503%	$254.9768	$254.98	$255.00	$255.00
Purchase #4	$249.69	7.341%	$268.0197	$268.02	$268.00	$268.00
Purchase #5	$11.94	11.554%	$13.3195	$13.32	$13.30	$13.30
Purchase #6	$238.94	10.352%	$263.6751	$263.68	$263.70	$263.70
Purchase #7	$82.78	6.512%	$88.1706	$88.17	$88.15	$88.20
7 purchase totals =	$929.46		$1,013.0063	$1,013.02	$1,013.00	$1,013.10