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	$35.52	9.719%	$38.9722	$38.97	$38.95	$39.00
Purchase #2	$188.42	12.838%	$212.6094	$212.61	$212.60	$212.60
Purchase #3	$60.76	11.201%	$67.5657	$67.57	$67.55	$67.60
Purchase #4	$80.96	12.685%	$91.2298	$91.23	$91.25	$91.20
Purchase #5	$35.48	3.429%	$36.6966	$36.70	$36.70	$36.70
Purchase #6	$83.63	8.278%	$90.5529	$90.55	$90.55	$90.60
Purchase #7	$169.38	3.526%	$175.3523	$175.35	$175.35	$175.40
7 purchase totals =	$654.15		$712.9789	$712.98	$712.95	$713.10