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	$50.90	5.649%	$53.7753	$53.78	$53.80	$53.80
Purchase #2	$95.57	11.222%	$106.2949	$106.29	$106.30	$106.30
Purchase #3	$99.48	13.150%	$112.5616	$112.56	$112.55	$112.60
Purchase #4	$140.59	9.392%	$153.7942	$153.79	$153.80	$153.80
Purchase #5	$211.32	4.538%	$220.9097	$220.91	$220.90	$220.90
Purchase #6	$20.49	12.618%	$23.0754	$23.08	$23.10	$23.10
Purchase #7	$85.45	5.285%	$89.966	$89.97	$89.95	$90.00
7 purchase totals =	$703.80		$760.3771	$760.38	$760.40	$760.50