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	$64.98	4.145%	$67.6734	$67.67	$67.65	$67.70
Purchase #2	$132.68	8.285%	$143.6725	$143.67	$143.65	$143.70
Purchase #3	$55.47	12.337%	$62.3133	$62.31	$62.30	$62.30
Purchase #4	$189.56	10.564%	$209.5851	$209.59	$209.60	$209.60
Purchase #5	$99.69	13.172%	$112.8212	$112.82	$112.80	$112.80
Purchase #6	$88.35	6.294%	$93.9107	$93.91	$93.90	$93.90
Purchase #7	$132.78	3.679%	$137.665	$137.67	$137.65	$137.70
7 purchase totals =	$763.51		$827.6412	$827.64	$827.55	$827.70