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	$92.33	8.510%	$100.1873	$100.19	$100.20	$100.20
Purchase #2	$112.93	5.375%	$119	$119.00	$119.00	$119.00
Purchase #3	$31.39	4.791%	$32.8939	$32.89	$32.90	$32.90
Purchase #4	$240.34	11.612%	$268.2483	$268.25	$268.25	$268.20
Purchase #5	$11.50	3.804%	$11.9375	$11.94	$11.95	$11.90
Purchase #6	$10.68	7.796%	$11.5126	$11.51	$11.50	$11.50
Purchase #7	$151.33	10.184%	$166.7414	$166.74	$166.75	$166.70
7 purchase totals =	$650.50		$710.5210	$710.52	$710.55	$710.40