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	$172.81	7.546%	$185.8502	$185.85	$185.85	$185.90
Purchase #2	$131.61	9.738%	$144.4262	$144.43	$144.45	$144.40
Purchase #3	$244.98	13.823%	$278.8436	$278.84	$278.85	$278.80
Purchase #4	$19.72	6.267%	$20.9559	$20.96	$20.95	$21.00
Purchase #5	$174.28	5.484%	$183.8375	$183.84	$183.85	$183.80
Purchase #6	$169.53	11.513%	$189.048	$189.05	$189.05	$189.00
Purchase #7	$9.90	3.108%	$10.2077	$10.21	$10.20	$10.20
7 purchase totals =	$922.83		$1,013.1691	$1,013.18	$1,013.20	$1,013.10