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	$160.36	3.744%	$166.3639	$166.36	$166.35	$166.40
Purchase #2	$104.65	4.602%	$109.466	$109.47	$109.45	$109.50
Purchase #3	$222.98	8.767%	$242.5287	$242.53	$242.55	$242.50
Purchase #4	$128.45	12.669%	$144.7233	$144.72	$144.70	$144.70
Purchase #5	$78.43	10.396%	$86.5836	$86.58	$86.60	$86.60
Purchase #6	$67.52	5.508%	$71.239	$71.24	$71.25	$71.20
Purchase #7	$33.61	9.576%	$36.8285	$36.83	$36.85	$36.80
7 purchase totals =	$796.00		$857.7330	$857.73	$857.75	$857.70