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	$170.73	3.261%	$176.2975	$176.30	$176.30	$176.30
Purchase #2	$159.89	7.587%	$172.0209	$172.02	$172.00	$172.00
Purchase #3	$64.96	10.366%	$71.6938	$71.69	$71.70	$71.70
Purchase #4	$250.48	9.607%	$274.5436	$274.54	$274.55	$274.50
Purchase #5	$113.69	8.362%	$123.1968	$123.20	$123.20	$123.20
Purchase #6	$185.49	4.353%	$193.5644	$193.56	$193.55	$193.60
Purchase #7	$24.59	11.420%	$27.3982	$27.40	$27.40	$27.40
7 purchase totals =	$969.83		$1,038.7152	$1,038.71	$1,038.70	$1,038.70