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	$33.60	11.454%	$37.4485	$37.45	$37.45	$37.40
Purchase #2	$22.56	7.793%	$24.3181	$24.32	$24.30	$24.30
Purchase #3	$244.37	13.141%	$276.4827	$276.48	$276.50	$276.50
Purchase #4	$37.53	13.326%	$42.5312	$42.53	$42.55	$42.50
Purchase #5	$212.77	6.421%	$226.432	$226.43	$226.45	$226.40
Purchase #6	$238.49	7.637%	$256.7035	$256.70	$256.70	$256.70
Purchase #7	$77.87	7.335%	$83.5818	$83.58	$83.60	$83.60
7 purchase totals =	$867.19		$947.4978	$947.49	$947.55	$947.40