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	$231.28	7.729%	$249.1556	$249.16	$249.15	$249.20
Purchase #2	$165.56	3.339%	$171.088	$171.09	$171.10	$171.10
Purchase #3	$148.88	13.461%	$168.9207	$168.92	$168.90	$168.90
Purchase #4	$45.68	12.783%	$51.5193	$51.52	$51.50	$51.50
Purchase #5	$179.86	3.296%	$185.7882	$185.79	$185.80	$185.80
Purchase #6	$122.43	6.438%	$130.312	$130.31	$130.30	$130.30
Purchase #7	$44.69	10.807%	$49.5196	$49.52	$49.50	$49.50
7 purchase totals =	$938.38		$1,006.3034	$1,006.31	$1,006.25	$1,006.30