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	$98.37	10.542%	$108.7402	$108.74	$108.75	$108.70
Purchase #2	$125.57	8.454%	$136.1857	$136.19	$136.20	$136.20
Purchase #3	$31.91	11.831%	$35.6853	$35.69	$35.70	$35.70
Purchase #4	$143.30	3.503%	$148.3198	$148.32	$148.30	$148.30
Purchase #5	$19.60	10.824%	$21.7215	$21.72	$21.70	$21.70
Purchase #6	$75.61	9.265%	$82.6153	$82.62	$82.60	$82.60
Purchase #7	$112.89	13.230%	$127.8253	$127.83	$127.85	$127.80
7 purchase totals =	$607.25		$661.0931	$661.11	$661.10	$661.00