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	$234.75	13.692%	$266.892	$266.89	$266.90	$266.90
Purchase #2	$128.95	8.531%	$139.9507	$139.95	$139.95	$140.00
Purchase #3	$217.70	3.304%	$224.8928	$224.89	$224.90	$224.90
Purchase #4	$58.75	4.524%	$61.4079	$61.41	$61.40	$61.40
Purchase #5	$42.37	3.598%	$43.8945	$43.89	$43.90	$43.90
Purchase #6	$200.95	3.869%	$208.7248	$208.72	$208.70	$208.70
Purchase #7	$219.39	10.670%	$242.7989	$242.80	$242.80	$242.80
7 purchase totals =	$1,102.86		$1,188.5616	$1,188.55	$1,188.55	$1,188.60