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	$29.39	12.113%	$32.95	$32.95	$32.95	$33.00
Purchase #2	$37.72	5.708%	$39.8731	$39.87	$39.85	$39.90
Purchase #3	$189.80	13.751%	$215.8994	$215.90	$215.90	$215.90
Purchase #4	$92.84	13.732%	$105.5888	$105.59	$105.60	$105.60
Purchase #5	$142.81	5.351%	$150.4518	$150.45	$150.45	$150.50
Purchase #6	$44.48	6.212%	$47.2431	$47.24	$47.25	$47.20
Purchase #7	$212.27	7.737%	$228.6933	$228.69	$228.70	$228.70
7 purchase totals =	$749.31		$820.6995	$820.69	$820.70	$820.80