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	$153.88	3.680%	$159.5428	$159.54	$159.55	$159.50
Purchase #2	$170.34	5.860%	$180.3219	$180.32	$180.30	$180.30
Purchase #3	$76.77	11.770%	$85.8058	$85.81	$85.80	$85.80
Purchase #4	$144.98	7.123%	$155.3069	$155.31	$155.30	$155.30
Purchase #5	$164.83	13.468%	$187.0293	$187.03	$187.05	$187.00
Purchase #6	$206.36	3.471%	$213.5228	$213.52	$213.50	$213.50
Purchase #7	$241.27	8.170%	$260.9818	$260.98	$261.00	$261.00
7 purchase totals =	$1,158.43		$1,242.5113	$1,242.51	$1,242.50	$1,242.40