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	$209.54	6.156%	$222.4393	$222.44	$222.45	$222.40
Purchase #2	$250.54	13.412%	$284.1424	$284.14	$284.15	$284.10
Purchase #3	$176.76	3.105%	$182.2484	$182.25	$182.25	$182.20
Purchase #4	$103.78	12.166%	$116.4059	$116.41	$116.40	$116.40
Purchase #5	$46.96	10.476%	$51.8795	$51.88	$51.90	$51.90
Purchase #6	$108.57	3.520%	$112.3917	$112.39	$112.40	$112.40
Purchase #7	$170.67	9.427%	$186.7591	$186.76	$186.75	$186.80
7 purchase totals =	$1,066.82		$1,156.2663	$1,156.27	$1,156.30	$1,156.20