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	$114.66	13.810%	$130.4945	$130.49	$130.50	$130.50
Purchase #2	$53.77	10.581%	$59.4594	$59.46	$59.45	$59.50
Purchase #3	$248.58	8.599%	$269.9554	$269.96	$269.95	$270.00
Purchase #4	$42.81	6.107%	$45.4244	$45.42	$45.40	$45.40
Purchase #5	$195.42	10.227%	$215.4056	$215.41	$215.40	$215.40
Purchase #6	$38.94	13.508%	$44.2	$44.20	$44.20	$44.20
Purchase #7	$226.53	8.396%	$245.5495	$245.55	$245.55	$245.50
7 purchase totals =	$920.71		$1,010.4888	$1,010.49	$1,010.45	$1,010.50