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	$149.97	4.383%	$156.5432	$156.54	$156.55	$156.50
Purchase #2	$52.70	13.626%	$59.8809	$59.88	$59.90	$59.90
Purchase #3	$72.90	7.329%	$78.2428	$78.24	$78.25	$78.20
Purchase #4	$194.61	10.275%	$214.6062	$214.61	$214.60	$214.60
Purchase #5	$179.25	11.679%	$200.1846	$200.18	$200.20	$200.20
Purchase #6	$159.98	7.460%	$171.9145	$171.91	$171.90	$171.90
Purchase #7	$168.36	3.390%	$174.0674	$174.07	$174.05	$174.10
7 purchase totals =	$977.77		$1,055.4396	$1,055.43	$1,055.45	$1,055.40