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	$141.94	3.137%	$146.3927	$146.39	$146.40	$146.40
Purchase #2	$238.91	4.798%	$250.3729	$250.37	$250.35	$250.40
Purchase #3	$67.30	13.781%	$76.5746	$76.57	$76.55	$76.60
Purchase #4	$160.50	5.240%	$168.9102	$168.91	$168.90	$168.90
Purchase #5	$89.77	13.125%	$101.5523	$101.55	$101.55	$101.60
Purchase #6	$19.64	5.535%	$20.7271	$20.73	$20.75	$20.70
Purchase #7	$143.75	3.253%	$148.4262	$148.43	$148.45	$148.40
7 purchase totals =	$861.81		$912.9560	$912.95	$912.95	$913.00