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	$107.73	3.107%	$111.0772	$111.08	$111.10	$111.10
Purchase #2	$93.86	8.145%	$101.5049	$101.50	$101.50	$101.50
Purchase #3	$150.62	8.696%	$163.7179	$163.72	$163.70	$163.70
Purchase #4	$85.46	6.375%	$90.9081	$90.91	$90.90	$90.90
Purchase #5	$243.83	12.114%	$273.3676	$273.37	$273.35	$273.40
Purchase #6	$26.40	12.185%	$29.6168	$29.62	$29.60	$29.60
Purchase #7	$132.90	8.250%	$143.8643	$143.86	$143.85	$143.90
7 purchase totals =	$840.80		$914.0568	$914.06	$914.00	$914.10