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	$29.99	10.853%	$33.2448	$33.24	$33.25	$33.20
Purchase #2	$184.71	6.780%	$197.2333	$197.23	$197.25	$197.20
Purchase #3	$137.56	11.192%	$152.9557	$152.96	$152.95	$153.00
Purchase #4	$64.96	3.386%	$67.1595	$67.16	$67.15	$67.20
Purchase #5	$105.67	5.770%	$111.7672	$111.77	$111.75	$111.80
Purchase #6	$213.91	12.470%	$240.5846	$240.58	$240.60	$240.60
Purchase #7	$27.39	4.484%	$28.6182	$28.62	$28.60	$28.60
7 purchase totals =	$764.19		$831.5633	$831.56	$831.55	$831.60