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	$86.78	4.269%	$90.4846	$90.48	$90.50	$90.50
Purchase #2	$187.73	12.526%	$211.2451	$211.25	$211.25	$211.20
Purchase #3	$147.84	9.810%	$162.3431	$162.34	$162.35	$162.30
Purchase #4	$117.35	5.260%	$123.5226	$123.52	$123.50	$123.50
Purchase #5	$209.78	4.117%	$218.4166	$218.42	$218.40	$218.40
Purchase #6	$234.55	13.331%	$265.8179	$265.82	$265.80	$265.80
Purchase #7	$67.60	9.699%	$74.1565	$74.16	$74.15	$74.20
7 purchase totals =	$1,051.63		$1,145.9864	$1,145.99	$1,145.95	$1,145.90