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	$207.32	5.318%	$218.3453	$218.35	$218.35	$218.30
Purchase #2	$29.79	4.826%	$31.2277	$31.23	$31.25	$31.20
Purchase #3	$80.43	7.268%	$86.2757	$86.28	$86.30	$86.30
Purchase #4	$37.40	13.365%	$42.3985	$42.40	$42.40	$42.40
Purchase #5	$91.73	8.854%	$99.8518	$99.85	$99.85	$99.90
Purchase #6	$74.80	12.641%	$84.2555	$84.26	$84.25	$84.30
Purchase #7	$29.83	7.471%	$32.0586	$32.06	$32.05	$32.10
7 purchase totals =	$551.30		$594.4131	$594.43	$594.45	$594.50