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	$30.61	6.387%	$32.5651	$32.57	$32.55	$32.60
Purchase #2	$156.96	4.588%	$164.1613	$164.16	$164.15	$164.20
Purchase #3	$127.56	12.264%	$143.204	$143.20	$143.20	$143.20
Purchase #4	$161.41	3.783%	$167.5161	$167.52	$167.50	$167.50
Purchase #5	$170.81	6.151%	$181.3165	$181.32	$181.30	$181.30
Purchase #6	$236.44	5.858%	$250.2907	$250.29	$250.30	$250.30
Purchase #7	$28.35	11.338%	$31.5643	$31.56	$31.55	$31.60
7 purchase totals =	$912.14		$970.6180	$970.62	$970.55	$970.70