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	$91.71	8.563%	$99.5631	$99.56	$99.55	$99.60
Purchase #2	$162.92	13.686%	$185.2172	$185.22	$185.20	$185.20
Purchase #3	$134.69	3.568%	$139.4957	$139.50	$139.50	$139.50
Purchase #4	$213.59	6.426%	$227.3153	$227.32	$227.30	$227.30
Purchase #5	$141.33	8.493%	$153.3332	$153.33	$153.35	$153.30
Purchase #6	$180.53	11.105%	$200.5779	$200.58	$200.60	$200.60
Purchase #7	$231.48	8.116%	$250.2669	$250.27	$250.25	$250.30
7 purchase totals =	$1,156.25		$1,255.7693	$1,255.78	$1,255.75	$1,255.80