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	$166.30	10.132%	$183.1495	$183.15	$183.15	$183.10
Purchase #2	$153.36	5.692%	$162.0893	$162.09	$162.10	$162.10
Purchase #3	$143.64	8.589%	$155.9772	$155.98	$156.00	$156.00
Purchase #4	$218.79	9.516%	$239.6101	$239.61	$239.60	$239.60
Purchase #5	$72.53	7.562%	$78.0147	$78.01	$78.00	$78.00
Purchase #6	$54.38	13.474%	$61.7072	$61.71	$61.70	$61.70
Purchase #7	$184.89	6.156%	$196.2718	$196.27	$196.25	$196.30
7 purchase totals =	$993.89		$1,076.8198	$1,076.82	$1,076.80	$1,076.80