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	$159.37	5.288%	$167.7975	$167.80	$167.80	$167.80
Purchase #2	$155.57	8.391%	$168.6239	$168.62	$168.60	$168.60
Purchase #3	$143.50	10.726%	$158.8918	$158.89	$158.90	$158.90
Purchase #4	$58.80	12.707%	$66.2717	$66.27	$66.25	$66.30
Purchase #5	$243.39	5.530%	$256.8495	$256.85	$256.85	$256.80
Purchase #6	$110.33	10.446%	$121.8551	$121.86	$121.85	$121.90
Purchase #7	$64.54	7.673%	$69.4922	$69.49	$69.50	$69.50
7 purchase totals =	$935.50		$1,009.7817	$1,009.78	$1,009.75	$1,009.80