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	$209.56	7.356%	$224.9752	$224.98	$225.00	$225.00
Purchase #2	$208.58	11.253%	$232.0515	$232.05	$232.05	$232.10
Purchase #3	$127.69	13.483%	$144.9064	$144.91	$144.90	$144.90
Purchase #4	$86.75	4.351%	$90.5245	$90.52	$90.50	$90.50
Purchase #5	$67.70	6.788%	$72.2955	$72.30	$72.30	$72.30
Purchase #6	$236.93	5.334%	$249.5678	$249.57	$249.55	$249.60
Purchase #7	$67.86	3.297%	$70.0973	$70.10	$70.10	$70.10
7 purchase totals =	$1,005.07		$1,084.4182	$1,084.43	$1,084.40	$1,084.50