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	$159.91	7.429%	$171.7897	$171.79	$171.80	$171.80
Purchase #2	$42.64	6.683%	$45.4896	$45.49	$45.50	$45.50
Purchase #3	$102.96	7.102%	$110.2722	$110.27	$110.25	$110.30
Purchase #4	$149.53	12.699%	$168.5188	$168.52	$168.50	$168.50
Purchase #5	$176.39	12.252%	$198.0013	$198.00	$198.00	$198.00
Purchase #6	$110.69	9.678%	$121.4026	$121.40	$121.40	$121.40
Purchase #7	$179.58	4.780%	$188.1639	$188.16	$188.15	$188.20
7 purchase totals =	$921.70		$1,003.6381	$1,003.63	$1,003.60	$1,003.70