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	$170.78	11.775%	$190.8893	$190.89	$190.90	$190.90
Purchase #2	$82.46	11.353%	$91.8217	$91.82	$91.80	$91.80
Purchase #3	$176.39	7.640%	$189.8662	$189.87	$189.85	$189.90
Purchase #4	$168.32	12.839%	$189.9306	$189.93	$189.95	$189.90
Purchase #5	$198.42	10.528%	$219.3097	$219.31	$219.30	$219.30
Purchase #6	$136.42	10.748%	$151.0824	$151.08	$151.10	$151.10
Purchase #7	$120.28	11.805%	$134.4791	$134.48	$134.50	$134.50
7 purchase totals =	$1,053.07		$1,167.3790	$1,167.38	$1,167.40	$1,167.40