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	$19.72	4.659%	$20.6388	$20.64	$20.65	$20.60
Purchase #2	$208.52	11.526%	$232.554	$232.55	$232.55	$232.60
Purchase #3	$170.83	5.770%	$180.6869	$180.69	$180.70	$180.70
Purchase #4	$200.70	9.817%	$220.4027	$220.40	$220.40	$220.40
Purchase #5	$52.84	12.121%	$59.2447	$59.24	$59.25	$59.20
Purchase #6	$157.94	11.161%	$175.5677	$175.57	$175.55	$175.60
Purchase #7	$106.67	7.295%	$114.4516	$114.45	$114.45	$114.50
7 purchase totals =	$917.22		$1,003.5464	$1,003.54	$1,003.55	$1,003.60