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	$145.90	4.553%	$152.5428	$152.54	$152.55	$152.50
Purchase #2	$165.88	8.819%	$180.509	$180.51	$180.50	$180.50
Purchase #3	$33.86	5.426%	$35.6972	$35.70	$35.70	$35.70
Purchase #4	$136.47	10.311%	$150.5414	$150.54	$150.55	$150.50
Purchase #5	$23.70	6.399%	$25.2166	$25.22	$25.20	$25.20
Purchase #6	$205.71	10.630%	$227.577	$227.58	$227.60	$227.60
Purchase #7	$132.83	6.154%	$141.0044	$141.00	$141.00	$141.00
7 purchase totals =	$844.35		$913.0884	$913.09	$913.10	$913.00