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	$136.25	6.491%	$145.094	$145.09	$145.10	$145.10
Purchase #2	$65.51	6.793%	$69.9601	$69.96	$69.95	$70.00
Purchase #3	$80.88	11.395%	$90.0963	$90.10	$90.10	$90.10
Purchase #4	$119.57	11.454%	$133.2655	$133.27	$133.25	$133.30
Purchase #5	$99.41	9.564%	$108.9176	$108.92	$108.90	$108.90
Purchase #6	$219.71	10.197%	$242.1138	$242.11	$242.10	$242.10
Purchase #7	$82.67	7.798%	$89.1166	$89.12	$89.10	$89.10
7 purchase totals =	$804.00		$878.5639	$878.57	$878.50	$878.60