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	$99.70	3.583%	$103.2723	$103.27	$103.25	$103.30
Purchase #2	$57.86	13.483%	$65.6613	$65.66	$65.65	$65.70
Purchase #3	$18.81	7.308%	$20.1846	$20.18	$20.20	$20.20
Purchase #4	$245.64	12.303%	$275.8611	$275.86	$275.85	$275.90
Purchase #5	$215.82	8.741%	$234.6848	$234.68	$234.70	$234.70
Purchase #6	$113.39	7.160%	$121.5087	$121.51	$121.50	$121.50
Purchase #7	$109.54	12.554%	$123.2917	$123.29	$123.30	$123.30
7 purchase totals =	$860.76		$944.4645	$944.45	$944.45	$944.60