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	$119.78	5.370%	$126.2122	$126.21	$126.20	$126.20
Purchase #2	$105.69	10.616%	$116.9101	$116.91	$116.90	$116.90
Purchase #3	$82.94	9.482%	$90.8044	$90.80	$90.80	$90.80
Purchase #4	$36.27	7.118%	$38.8517	$38.85	$38.85	$38.90
Purchase #5	$30.98	9.756%	$34.0024	$34.00	$34.00	$34.00
Purchase #6	$232.47	7.799%	$250.6003	$250.60	$250.60	$250.60
Purchase #7	$7.33	10.361%	$8.0895	$8.09	$8.10	$8.10
7 purchase totals =	$615.46		$665.4706	$665.46	$665.45	$665.50