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	$94.34	9.317%	$103.1297	$103.13	$103.15	$103.10
Purchase #2	$91.85	10.476%	$101.4722	$101.47	$101.45	$101.50
Purchase #3	$222.54	12.106%	$249.4807	$249.48	$249.50	$249.50
Purchase #4	$142.41	7.339%	$152.8615	$152.86	$152.85	$152.90
Purchase #5	$135.49	6.726%	$144.6031	$144.60	$144.60	$144.60
Purchase #6	$162.74	10.122%	$179.2125	$179.21	$179.20	$179.20
Purchase #7	$158.31	13.827%	$180.1995	$180.20	$180.20	$180.20
7 purchase totals =	$1,007.68		$1,110.9592	$1,110.95	$1,110.95	$1,111.00