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	$12.61	7.577%	$13.5655	$13.57	$13.55	$13.60
Purchase #2	$101.39	8.365%	$109.8713	$109.87	$109.85	$109.90
Purchase #3	$86.82	12.548%	$97.7142	$97.71	$97.70	$97.70
Purchase #4	$235.81	4.262%	$245.8602	$245.86	$245.85	$245.90
Purchase #5	$139.98	8.784%	$152.2758	$152.28	$152.30	$152.30
Purchase #6	$121.60	7.196%	$130.3503	$130.35	$130.35	$130.40
Purchase #7	$133.90	12.489%	$150.6228	$150.62	$150.60	$150.60
7 purchase totals =	$832.11		$900.2601	$900.26	$900.20	$900.40