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	$185.36	7.723%	$199.6754	$199.68	$199.70	$199.70
Purchase #2	$90.65	8.153%	$98.0407	$98.04	$98.05	$98.00
Purchase #3	$100.85	8.733%	$109.6572	$109.66	$109.65	$109.70
Purchase #4	$54.94	8.499%	$59.6094	$59.61	$59.60	$59.60
Purchase #5	$74.80	5.154%	$78.6552	$78.66	$78.65	$78.70
Purchase #6	$61.44	9.710%	$67.4058	$67.41	$67.40	$67.40
Purchase #7	$51.48	8.647%	$55.9315	$55.93	$55.95	$55.90
7 purchase totals =	$619.52		$668.9752	$668.99	$669.00	$669.00