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	$91.60	11.850%	$102.4546	$102.45	$102.45	$102.50
Purchase #2	$28.58	3.369%	$29.5429	$29.54	$29.55	$29.50
Purchase #3	$178.62	6.276%	$189.8302	$189.83	$189.85	$189.80
Purchase #4	$110.47	3.722%	$114.5817	$114.58	$114.60	$114.60
Purchase #5	$120.79	9.230%	$131.9389	$131.94	$131.95	$131.90
Purchase #6	$55.35	9.111%	$60.3929	$60.39	$60.40	$60.40
Purchase #7	$17.48	10.282%	$19.2773	$19.28	$19.30	$19.30
7 purchase totals =	$602.89		$648.0185	$648.01	$648.10	$648.00