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	$133.52	8.802%	$145.2724	$145.27	$145.25	$145.30
Purchase #2	$105.34	5.726%	$111.3718	$111.37	$111.35	$111.40
Purchase #3	$102.96	10.394%	$113.6617	$113.66	$113.65	$113.70
Purchase #4	$79.63	5.143%	$83.7254	$83.73	$83.75	$83.70
Purchase #5	$24.89	10.141%	$27.4141	$27.41	$27.40	$27.40
Purchase #6	$13.31	6.166%	$14.1307	$14.13	$14.15	$14.10
Purchase #7	$95.68	6.540%	$101.9375	$101.94	$101.95	$101.90
7 purchase totals =	$555.33		$597.5136	$597.51	$597.50	$597.50