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	$86.41	3.440%	$89.3825	$89.38	$89.40	$89.40
Purchase #2	$137.50	12.193%	$154.2654	$154.27	$154.25	$154.30
Purchase #3	$132.92	7.488%	$142.873	$142.87	$142.85	$142.90
Purchase #4	$184.89	12.342%	$207.7091	$207.71	$207.70	$207.70
Purchase #5	$210.30	11.517%	$234.5203	$234.52	$234.50	$234.50
Purchase #6	$31.99	5.482%	$33.7437	$33.74	$33.75	$33.70
Purchase #7	$107.31	11.300%	$119.436	$119.44	$119.45	$119.40
7 purchase totals =	$891.32		$981.9300	$981.93	$981.90	$981.90