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	$152.41	13.372%	$172.7903	$172.79	$172.80	$172.80
Purchase #2	$200.99	13.663%	$228.4513	$228.45	$228.45	$228.50
Purchase #3	$38.71	8.167%	$41.8714	$41.87	$41.85	$41.90
Purchase #4	$34.84	6.256%	$37.0196	$37.02	$37.00	$37.00
Purchase #5	$40.27	10.779%	$44.6107	$44.61	$44.60	$44.60
Purchase #6	$64.63	3.870%	$67.1312	$67.13	$67.15	$67.10
Purchase #7	$71.97	4.668%	$75.3296	$75.33	$75.35	$75.30
7 purchase totals =	$603.82		$667.2041	$667.20	$667.20	$667.20