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	$215.63	10.457%	$238.1784	$238.18	$238.20	$238.20
Purchase #2	$237.75	11.366%	$264.7727	$264.77	$264.75	$264.80
Purchase #3	$93.83	6.264%	$99.7075	$99.71	$99.70	$99.70
Purchase #4	$229.54	5.279%	$241.6574	$241.66	$241.65	$241.70
Purchase #5	$12.47	9.292%	$13.6287	$13.63	$13.65	$13.60
Purchase #6	$85.67	4.471%	$89.5003	$89.50	$89.50	$89.50
Purchase #7	$27.52	3.783%	$28.5611	$28.56	$28.55	$28.60
7 purchase totals =	$902.41		$976.0061	$976.01	$976.00	$976.10