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	$99.94	4.453%	$104.3903	$104.39	$104.40	$104.40
Purchase #2	$119.93	9.395%	$131.1974	$131.20	$131.20	$131.20
Purchase #3	$117.38	12.771%	$132.3706	$132.37	$132.35	$132.40
Purchase #4	$216.79	12.178%	$243.1907	$243.19	$243.20	$243.20
Purchase #5	$22.72	11.569%	$25.3485	$25.35	$25.35	$25.30
Purchase #6	$182.47	7.424%	$196.0166	$196.02	$196.00	$196.00
Purchase #7	$80.91	10.180%	$89.1466	$89.15	$89.15	$89.10
7 purchase totals =	$840.14		$921.6607	$921.67	$921.65	$921.60