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	$87.78	4.418%	$91.6581	$91.66	$91.65	$91.70
Purchase #2	$194.61	9.317%	$212.7418	$212.74	$212.75	$212.70
Purchase #3	$37.33	7.152%	$39.9998	$40.00	$40.00	$40.00
Purchase #4	$19.87	10.357%	$21.9279	$21.93	$21.95	$21.90
Purchase #5	$99.63	4.244%	$103.8583	$103.86	$103.85	$103.90
Purchase #6	$244.88	3.389%	$253.179	$253.18	$253.20	$253.20
Purchase #7	$69.94	3.796%	$72.5949	$72.59	$72.60	$72.60
7 purchase totals =	$754.04		$795.9598	$795.96	$796.00	$796.00