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	$150.43	6.769%	$160.6126	$160.61	$160.60	$160.60
Purchase #2	$139.27	11.591%	$155.4128	$155.41	$155.40	$155.40
Purchase #3	$82.53	10.478%	$91.1775	$91.18	$91.20	$91.20
Purchase #4	$195.80	6.685%	$208.8892	$208.89	$208.90	$208.90
Purchase #5	$158.69	13.596%	$180.2655	$180.27	$180.25	$180.30
Purchase #6	$78.68	9.168%	$85.8934	$85.89	$85.90	$85.90
Purchase #7	$128.90	4.294%	$134.435	$134.44	$134.45	$134.40
7 purchase totals =	$934.30		$1,016.6860	$1,016.69	$1,016.70	$1,016.70