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	$97.98	7.589%	$105.4157	$105.42	$105.40	$105.40
Purchase #2	$158.58	5.831%	$167.8268	$167.83	$167.85	$167.80
Purchase #3	$119.82	9.657%	$131.391	$131.39	$131.40	$131.40
Purchase #4	$134.69	7.182%	$144.3634	$144.36	$144.35	$144.40
Purchase #5	$105.72	6.439%	$112.5273	$112.53	$112.55	$112.50
Purchase #6	$226.57	12.212%	$254.2387	$254.24	$254.25	$254.20
Purchase #7	$39.96	6.712%	$42.6421	$42.64	$42.65	$42.60
7 purchase totals =	$883.32		$958.4050	$958.41	$958.45	$958.30