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	$131.68	12.510%	$148.1532	$148.15	$148.15	$148.20
Purchase #2	$38.99	7.809%	$42.0347	$42.03	$42.05	$42.00
Purchase #3	$140.80	12.767%	$158.7759	$158.78	$158.80	$158.80
Purchase #4	$127.33	9.294%	$139.1641	$139.16	$139.15	$139.20
Purchase #5	$159.85	8.303%	$173.1223	$173.12	$173.10	$173.10
Purchase #6	$50.50	4.494%	$52.7695	$52.77	$52.75	$52.80
Purchase #7	$29.34	8.468%	$31.8245	$31.82	$31.80	$31.80
7 purchase totals =	$678.49		$745.8442	$745.83	$745.80	$745.90