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	$150.30	6.360%	$159.8591	$159.86	$159.85	$159.90
Purchase #2	$178.61	4.724%	$187.0475	$187.05	$187.05	$187.00
Purchase #3	$129.58	3.443%	$134.0414	$134.04	$134.05	$134.00
Purchase #4	$89.43	12.411%	$100.5292	$100.53	$100.55	$100.50
Purchase #5	$174.57	4.586%	$182.5758	$182.58	$182.60	$182.60
Purchase #6	$48.72	6.220%	$51.7504	$51.75	$51.75	$51.80
Purchase #7	$233.31	7.777%	$251.4545	$251.45	$251.45	$251.50
7 purchase totals =	$1,004.52		$1,067.2579	$1,067.26	$1,067.30	$1,067.30