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	$63.32	8.111%	$68.4559	$68.46	$68.45	$68.50
Purchase #2	$123.59	13.415%	$140.1696	$140.17	$140.15	$140.20
Purchase #3	$176.82	12.263%	$198.5034	$198.50	$198.50	$198.50
Purchase #4	$32.96	4.696%	$34.5078	$34.51	$34.50	$34.50
Purchase #5	$148.66	5.125%	$156.2788	$156.28	$156.30	$156.30
Purchase #6	$229.32	6.110%	$243.3315	$243.33	$243.35	$243.30
Purchase #7	$64.95	10.307%	$71.6444	$71.64	$71.65	$71.60
7 purchase totals =	$839.62		$912.8914	$912.89	$912.90	$912.90