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	$209.34	12.517%	$235.5431	$235.54	$235.55	$235.50
Purchase #2	$241.70	9.711%	$265.1715	$265.17	$265.15	$265.20
Purchase #3	$202.30	11.435%	$225.433	$225.43	$225.45	$225.40
Purchase #4	$145.70	12.833%	$164.3977	$164.40	$164.40	$164.40
Purchase #5	$72.92	9.727%	$80.0129	$80.01	$80.00	$80.00
Purchase #6	$159.39	5.789%	$168.6171	$168.62	$168.60	$168.60
Purchase #7	$134.98	12.285%	$151.5623	$151.56	$151.55	$151.60
7 purchase totals =	$1,166.33		$1,290.7376	$1,290.73	$1,290.70	$1,290.70