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	$137.85	4.786%	$144.4475	$144.45	$144.45	$144.40
Purchase #2	$200.37	11.286%	$222.9838	$222.98	$223.00	$223.00
Purchase #3	$182.77	7.431%	$196.3516	$196.35	$196.35	$196.40
Purchase #4	$183.48	4.170%	$191.1311	$191.13	$191.15	$191.10
Purchase #5	$79.56	7.299%	$85.3671	$85.37	$85.35	$85.40
Purchase #6	$70.68	13.437%	$80.1773	$80.18	$80.20	$80.20
Purchase #7	$14.73	7.478%	$15.8315	$15.83	$15.85	$15.80
7 purchase totals =	$869.44		$936.2899	$936.29	$936.35	$936.30