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	$87.39	5.145%	$91.8862	$91.89	$91.90	$91.90
Purchase #2	$42.81	12.174%	$48.0217	$48.02	$48.00	$48.00
Purchase #3	$132.92	4.684%	$139.146	$139.15	$139.15	$139.10
Purchase #4	$86.93	4.585%	$90.9157	$90.92	$90.90	$90.90
Purchase #5	$28.58	10.361%	$31.5412	$31.54	$31.55	$31.50
Purchase #6	$116.88	4.807%	$122.4984	$122.50	$122.50	$122.50
Purchase #7	$44.49	12.577%	$50.0855	$50.09	$50.10	$50.10
7 purchase totals =	$540.00		$574.0947	$574.11	$574.10	$574.00