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	$144.56	10.797%	$160.1681	$160.17	$160.15	$160.20
Purchase #2	$216.38	7.151%	$231.8533	$231.85	$231.85	$231.90
Purchase #3	$173.46	7.678%	$186.7783	$186.78	$186.80	$186.80
Purchase #4	$173.82	7.809%	$187.3936	$187.39	$187.40	$187.40
Purchase #5	$74.44	3.733%	$77.2188	$77.22	$77.20	$77.20
Purchase #6	$94.46	13.110%	$106.8437	$106.84	$106.85	$106.80
Purchase #7	$222.96	12.232%	$250.2325	$250.23	$250.25	$250.20
7 purchase totals =	$1,100.08		$1,200.4883	$1,200.48	$1,200.50	$1,200.50