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	$239.99	10.591%	$265.4073	$265.41	$265.40	$265.40
Purchase #2	$105.74	9.570%	$115.8593	$115.86	$115.85	$115.90
Purchase #3	$177.83	10.202%	$195.9722	$195.97	$195.95	$196.00
Purchase #4	$90.79	11.150%	$100.9131	$100.91	$100.90	$100.90
Purchase #5	$21.89	7.458%	$23.5226	$23.52	$23.50	$23.50
Purchase #6	$175.87	5.550%	$185.6308	$185.63	$185.65	$185.60
Purchase #7	$224.95	13.614%	$255.5747	$255.57	$255.55	$255.60
7 purchase totals =	$1,037.06		$1,142.8800	$1,142.87	$1,142.80	$1,142.90