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	$97.73	11.612%	$109.0784	$109.08	$109.10	$109.10
Purchase #2	$203.69	4.211%	$212.2674	$212.27	$212.25	$212.30
Purchase #3	$139.91	4.666%	$146.4382	$146.44	$146.45	$146.40
Purchase #4	$78.54	13.616%	$89.234	$89.23	$89.25	$89.20
Purchase #5	$40.29	4.828%	$42.2352	$42.24	$42.25	$42.20
Purchase #6	$237.40	6.515%	$252.8666	$252.87	$252.85	$252.90
Purchase #7	$46.25	3.776%	$47.9964	$48.00	$48.00	$48.00
7 purchase totals =	$843.81		$900.1162	$900.13	$900.15	$900.10