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	$245.79	10.691%	$272.0674	$272.07	$272.05	$272.10
Purchase #2	$56.25	6.103%	$59.6829	$59.68	$59.70	$59.70
Purchase #3	$83.51	7.435%	$89.719	$89.72	$89.70	$89.70
Purchase #4	$172.70	7.759%	$186.0998	$186.10	$186.10	$186.10
Purchase #5	$159.92	9.109%	$174.4871	$174.49	$174.50	$174.50
Purchase #6	$32.69	8.556%	$35.487	$35.49	$35.50	$35.50
Purchase #7	$36.26	12.717%	$40.8712	$40.87	$40.85	$40.90
7 purchase totals =	$787.12		$858.4144	$858.42	$858.40	$858.50