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	$170.25	12.345%	$191.2674	$191.27	$191.25	$191.30
Purchase #2	$205.55	8.292%	$222.5942	$222.59	$222.60	$222.60
Purchase #3	$92.79	11.814%	$103.7522	$103.75	$103.75	$103.80
Purchase #4	$20.26	5.837%	$21.4426	$21.44	$21.45	$21.40
Purchase #5	$196.33	13.299%	$222.4399	$222.44	$222.45	$222.40
Purchase #6	$234.79	8.856%	$255.583	$255.58	$255.60	$255.60
Purchase #7	$55.73	12.116%	$62.4822	$62.48	$62.50	$62.50
7 purchase totals =	$975.70		$1,079.5615	$1,079.55	$1,079.60	$1,079.60