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	$215.56	6.353%	$229.2545	$229.25	$229.25	$229.30
Purchase #2	$166.64	12.551%	$187.555	$187.56	$187.55	$187.60
Purchase #3	$54.87	13.511%	$62.2835	$62.28	$62.30	$62.30
Purchase #4	$41.34	6.149%	$43.882	$43.88	$43.90	$43.90
Purchase #5	$90.54	9.233%	$98.8996	$98.90	$98.90	$98.90
Purchase #6	$200.61	11.311%	$223.301	$223.30	$223.30	$223.30
Purchase #7	$42.91	3.519%	$44.42	$44.42	$44.40	$44.40
7 purchase totals =	$812.47		$889.5956	$889.59	$889.60	$889.70