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	$36.45	10.661%	$40.3359	$40.34	$40.35	$40.30
Purchase #2	$250.77	4.835%	$262.8947	$262.89	$262.90	$262.90
Purchase #3	$163.41	9.640%	$179.1627	$179.16	$179.15	$179.20
Purchase #4	$246.46	6.595%	$262.714	$262.71	$262.70	$262.70
Purchase #5	$74.85	11.311%	$83.3163	$83.32	$83.30	$83.30
Purchase #6	$162.34	5.856%	$171.8466	$171.85	$171.85	$171.80
Purchase #7	$152.86	9.459%	$167.319	$167.32	$167.30	$167.30
7 purchase totals =	$1,087.14		$1,167.5892	$1,167.59	$1,167.55	$1,167.50