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	$189.74	12.853%	$214.1273	$214.13	$214.15	$214.10
Purchase #2	$35.89	6.837%	$38.3438	$38.34	$38.35	$38.30
Purchase #3	$200.40	11.242%	$222.929	$222.93	$222.95	$222.90
Purchase #4	$176.71	7.236%	$189.4967	$189.50	$189.50	$189.50
Purchase #5	$9.95	4.179%	$10.3658	$10.37	$10.35	$10.40
Purchase #6	$46.61	13.303%	$52.8105	$52.81	$52.80	$52.80
Purchase #7	$150.49	9.181%	$164.3065	$164.31	$164.30	$164.30
7 purchase totals =	$809.79		$892.3796	$892.39	$892.40	$892.30