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	$80.70	6.535%	$85.9737	$85.97	$85.95	$86.00
Purchase #2	$90.51	8.443%	$98.1518	$98.15	$98.15	$98.20
Purchase #3	$143.71	3.515%	$148.7614	$148.76	$148.75	$148.80
Purchase #4	$201.77	11.155%	$224.2774	$224.28	$224.30	$224.30
Purchase #5	$70.30	4.612%	$73.5422	$73.54	$73.55	$73.50
Purchase #6	$168.42	10.102%	$185.4338	$185.43	$185.45	$185.40
Purchase #7	$38.33	5.513%	$40.4431	$40.44	$40.45	$40.40
7 purchase totals =	$793.74		$856.5834	$856.57	$856.60	$856.60