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	$32.48	7.504%	$34.9173	$34.92	$34.90	$34.90
Purchase #2	$117.95	4.464%	$123.2153	$123.22	$123.20	$123.20
Purchase #3	$184.67	10.141%	$203.3974	$203.40	$203.40	$203.40
Purchase #4	$190.27	3.234%	$196.4233	$196.42	$196.40	$196.40
Purchase #5	$37.33	4.295%	$38.9333	$38.93	$38.95	$38.90
Purchase #6	$226.29	6.409%	$240.7929	$240.79	$240.80	$240.80
Purchase #7	$156.75	9.529%	$171.6867	$171.69	$171.70	$171.70
7 purchase totals =	$945.74		$1,009.3662	$1,009.37	$1,009.35	$1,009.30