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	$227.85	12.464%	$256.2492	$256.25	$256.25	$256.20
Purchase #2	$185.42	6.157%	$196.8363	$196.84	$196.85	$196.80
Purchase #3	$27.99	12.529%	$31.4969	$31.50	$31.50	$31.50
Purchase #4	$19.28	11.618%	$21.52	$21.52	$21.50	$21.50
Purchase #5	$177.26	8.263%	$191.907	$191.91	$191.90	$191.90
Purchase #6	$7.97	3.180%	$8.2234	$8.22	$8.20	$8.20
Purchase #7	$127.39	13.337%	$144.38	$144.38	$144.40	$144.40
7 purchase totals =	$773.16		$850.6128	$850.62	$850.60	$850.50