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	$112.93	3.576%	$116.9684	$116.97	$116.95	$117.00
Purchase #2	$38.90	8.432%	$42.18	$42.18	$42.20	$42.20
Purchase #3	$195.39	7.244%	$209.5441	$209.54	$209.55	$209.50
Purchase #4	$37.32	13.695%	$42.431	$42.43	$42.45	$42.40
Purchase #5	$170.78	13.468%	$193.7807	$193.78	$193.80	$193.80
Purchase #6	$13.53	4.333%	$14.1163	$14.12	$14.10	$14.10
Purchase #7	$152.94	10.261%	$168.6332	$168.63	$168.65	$168.60
7 purchase totals =	$721.79		$787.6537	$787.65	$787.70	$787.60