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	$131.60	9.543%	$144.1586	$144.16	$144.15	$144.20
Purchase #2	$243.38	8.766%	$264.7147	$264.71	$264.70	$264.70
Purchase #3	$62.46	5.296%	$65.7679	$65.77	$65.75	$65.80
Purchase #4	$174.62	6.534%	$186.0297	$186.03	$186.05	$186.00
Purchase #5	$110.85	5.389%	$116.8237	$116.82	$116.80	$116.80
Purchase #6	$141.62	13.600%	$160.8803	$160.88	$160.90	$160.90
Purchase #7	$29.72	10.712%	$32.9036	$32.90	$32.90	$32.90
7 purchase totals =	$894.25		$971.2785	$971.27	$971.25	$971.30