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	$215.32	12.571%	$242.3879	$242.39	$242.40	$242.40
Purchase #2	$160.59	4.859%	$168.3931	$168.39	$168.40	$168.40
Purchase #3	$158.76	6.405%	$168.9286	$168.93	$168.95	$168.90
Purchase #4	$233.90	6.668%	$249.4965	$249.50	$249.50	$249.50
Purchase #5	$96.89	3.728%	$100.5021	$100.50	$100.50	$100.50
Purchase #6	$107.87	10.452%	$119.1446	$119.14	$119.15	$119.10
Purchase #7	$247.99	6.633%	$264.4392	$264.44	$264.45	$264.40
7 purchase totals =	$1,221.32		$1,313.2920	$1,313.29	$1,313.35	$1,313.20