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	$151.64	13.157%	$171.5913	$171.59	$171.60	$171.60
Purchase #2	$90.99	9.386%	$99.5303	$99.53	$99.55	$99.50
Purchase #3	$133.70	5.802%	$141.4573	$141.46	$141.45	$141.50
Purchase #4	$76.37	6.491%	$81.3272	$81.33	$81.35	$81.30
Purchase #5	$145.80	11.142%	$162.045	$162.05	$162.05	$162.00
Purchase #6	$86.53	7.658%	$93.1565	$93.16	$93.15	$93.20
Purchase #7	$150.67	4.593%	$157.5903	$157.59	$157.60	$157.60
7 purchase totals =	$835.70		$906.6979	$906.71	$906.75	$906.70