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	$67.62	4.692%	$70.7927	$70.79	$70.80	$70.80
Purchase #2	$82.43	10.140%	$90.7884	$90.79	$90.80	$90.80
Purchase #3	$194.77	9.837%	$213.9295	$213.93	$213.95	$213.90
Purchase #4	$194.94	10.670%	$215.7401	$215.74	$215.75	$215.70
Purchase #5	$22.52	13.791%	$25.6257	$25.63	$25.65	$25.60
Purchase #6	$100.65	8.707%	$109.4136	$109.41	$109.40	$109.40
Purchase #7	$33.85	11.150%	$37.6243	$37.62	$37.60	$37.60
7 purchase totals =	$696.78		$763.9143	$763.91	$763.95	$763.80