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	$27.69	3.869%	$28.7613	$28.76	$28.75	$28.80
Purchase #2	$138.25	3.147%	$142.6007	$142.60	$142.60	$142.60
Purchase #3	$39.95	9.694%	$43.8228	$43.82	$43.80	$43.80
Purchase #4	$166.70	9.708%	$182.8832	$182.88	$182.90	$182.90
Purchase #5	$149.84	6.296%	$159.2739	$159.27	$159.25	$159.30
Purchase #6	$95.48	13.733%	$108.5923	$108.59	$108.60	$108.60
Purchase #7	$36.73	10.724%	$40.6689	$40.67	$40.65	$40.70
7 purchase totals =	$654.64		$706.6031	$706.59	$706.55	$706.70