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	$115.49	7.459%	$124.1044	$124.10	$124.10	$124.10
Purchase #2	$108.83	8.628%	$118.2199	$118.22	$118.20	$118.20
Purchase #3	$241.46	12.188%	$270.8891	$270.89	$270.90	$270.90
Purchase #4	$51.77	8.426%	$56.1321	$56.13	$56.15	$56.10
Purchase #5	$20.36	7.632%	$21.9139	$21.91	$21.90	$21.90
Purchase #6	$222.74	4.831%	$233.5006	$233.50	$233.50	$233.50
Purchase #7	$158.80	6.776%	$169.5603	$169.56	$169.55	$169.60
7 purchase totals =	$919.45		$994.3203	$994.31	$994.30	$994.30