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	$225.41	13.163%	$255.0807	$255.08	$255.10	$255.10
Purchase #2	$109.95	13.766%	$125.0857	$125.09	$125.10	$125.10
Purchase #3	$19.71	4.663%	$20.6291	$20.63	$20.65	$20.60
Purchase #4	$133.85	12.684%	$150.8275	$150.83	$150.85	$150.80
Purchase #5	$73.51	13.382%	$83.3471	$83.35	$83.35	$83.30
Purchase #6	$78.31	5.850%	$82.8911	$82.89	$82.90	$82.90
Purchase #7	$183.74	4.302%	$191.6445	$191.64	$191.65	$191.60
7 purchase totals =	$824.48		$909.5057	$909.51	$909.60	$909.40