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	$132.82	5.276%	$139.8276	$139.83	$139.85	$139.80
Purchase #2	$28.87	7.399%	$31.0061	$31.01	$31.00	$31.00
Purchase #3	$173.34	3.544%	$179.4832	$179.48	$179.50	$179.50
Purchase #4	$178.41	7.377%	$191.5713	$191.57	$191.55	$191.60
Purchase #5	$53.56	5.244%	$56.3687	$56.37	$56.35	$56.40
Purchase #6	$221.72	7.471%	$238.2847	$238.28	$238.30	$238.30
Purchase #7	$97.48	8.309%	$105.5796	$105.58	$105.60	$105.60
7 purchase totals =	$886.20		$942.1212	$942.12	$942.15	$942.20