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	$147.78	11.870%	$165.3215	$165.32	$165.30	$165.30
Purchase #2	$19.50	7.263%	$20.9163	$20.92	$20.90	$20.90
Purchase #3	$176.96	13.704%	$201.2106	$201.21	$201.20	$201.20
Purchase #4	$103.50	8.156%	$111.9415	$111.94	$111.95	$111.90
Purchase #5	$13.46	9.567%	$14.7477	$14.75	$14.75	$14.70
Purchase #6	$83.59	8.839%	$90.9785	$90.98	$91.00	$91.00
Purchase #7	$242.26	12.847%	$273.3831	$273.38	$273.40	$273.40
7 purchase totals =	$787.05		$878.4992	$878.50	$878.50	$878.40