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	$46.43	13.548%	$52.7203	$52.72	$52.70	$52.70
Purchase #2	$112.56	9.838%	$123.6337	$123.63	$123.65	$123.60
Purchase #3	$199.62	9.398%	$218.3803	$218.38	$218.40	$218.40
Purchase #4	$68.55	6.443%	$72.9667	$72.97	$72.95	$73.00
Purchase #5	$148.60	5.354%	$156.556	$156.56	$156.55	$156.60
Purchase #6	$165.94	13.744%	$188.7468	$188.75	$188.75	$188.70
Purchase #7	$15.32	10.167%	$16.8776	$16.88	$16.90	$16.90
7 purchase totals =	$757.02		$829.8814	$829.89	$829.90	$829.90