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	$81.60	4.492%	$85.2655	$85.27	$85.25	$85.30
Purchase #2	$35.60	13.188%	$40.2949	$40.29	$40.30	$40.30
Purchase #3	$189.82	13.717%	$215.8576	$215.86	$215.85	$215.90
Purchase #4	$20.39	4.283%	$21.2633	$21.26	$21.25	$21.30
Purchase #5	$196.26	9.611%	$215.1225	$215.12	$215.10	$215.10
Purchase #6	$213.73	9.523%	$234.0835	$234.08	$234.10	$234.10
Purchase #7	$104.39	13.497%	$118.4795	$118.48	$118.50	$118.50
7 purchase totals =	$841.79		$930.3668	$930.36	$930.35	$930.50