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	$161.49	13.266%	$182.9133	$182.91	$182.90	$182.90
Purchase #2	$237.28	10.673%	$262.6049	$262.60	$262.60	$262.60
Purchase #3	$142.43	10.440%	$157.2997	$157.30	$157.30	$157.30
Purchase #4	$95.34	4.592%	$99.718	$99.72	$99.70	$99.70
Purchase #5	$38.58	3.265%	$39.8396	$39.84	$39.85	$39.80
Purchase #6	$71.87	9.507%	$78.7027	$78.70	$78.70	$78.70
Purchase #7	$20.78	3.338%	$21.4736	$21.47	$21.45	$21.50
7 purchase totals =	$767.77		$842.5518	$842.54	$842.50	$842.50