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	$120.55	5.454%	$127.1248	$127.12	$127.10	$127.10
Purchase #2	$102.40	9.255%	$111.8771	$111.88	$111.90	$111.90
Purchase #3	$8.45	11.814%	$9.4483	$9.45	$9.45	$9.40
Purchase #4	$71.25	11.250%	$79.2656	$79.27	$79.25	$79.30
Purchase #5	$218.55	10.579%	$241.6704	$241.67	$241.65	$241.70
Purchase #6	$59.46	10.117%	$65.4756	$65.48	$65.50	$65.50
Purchase #7	$197.46	11.427%	$220.0238	$220.02	$220.00	$220.00
7 purchase totals =	$778.12		$854.8856	$854.89	$854.85	$854.90