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	$93.78	5.703%	$99.1283	$99.13	$99.15	$99.10
Purchase #2	$177.36	8.385%	$192.2316	$192.23	$192.25	$192.20
Purchase #3	$237.62	4.718%	$248.8309	$248.83	$248.85	$248.80
Purchase #4	$128.79	10.661%	$142.5203	$142.52	$142.50	$142.50
Purchase #5	$205.39	3.687%	$212.9627	$212.96	$212.95	$213.00
Purchase #6	$250.27	10.627%	$276.8662	$276.87	$276.85	$276.90
Purchase #7	$63.51	6.707%	$67.7696	$67.77	$67.75	$67.80
7 purchase totals =	$1,156.72		$1,240.3096	$1,240.31	$1,240.30	$1,240.30