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	$159.36	12.168%	$178.7509	$178.75	$178.75	$178.80
Purchase #2	$128.69	8.513%	$139.6454	$139.65	$139.65	$139.60
Purchase #3	$50.66	12.787%	$57.1379	$57.14	$57.15	$57.10
Purchase #4	$139.55	3.565%	$144.525	$144.53	$144.55	$144.50
Purchase #5	$142.92	3.348%	$147.705	$147.71	$147.70	$147.70
Purchase #6	$197.40	4.822%	$206.9186	$206.92	$206.90	$206.90
Purchase #7	$198.47	13.776%	$225.8112	$225.81	$225.80	$225.80
7 purchase totals =	$1,017.05		$1,100.4940	$1,100.51	$1,100.50	$1,100.40