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	$75.54	7.334%	$81.0801	$81.08	$81.10	$81.10
Purchase #2	$162.93	12.824%	$183.8241	$183.82	$183.80	$183.80
Purchase #3	$140.64	13.512%	$159.6433	$159.64	$159.65	$159.60
Purchase #4	$70.61	11.682%	$78.8587	$78.86	$78.85	$78.90
Purchase #5	$234.57	11.794%	$262.2352	$262.24	$262.25	$262.20
Purchase #6	$250.67	7.531%	$269.548	$269.55	$269.55	$269.50
Purchase #7	$42.26	6.230%	$44.8928	$44.89	$44.90	$44.90
7 purchase totals =	$977.22		$1,080.0822	$1,080.08	$1,080.10	$1,080.00