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	$80.91	11.645%	$90.332	$90.33	$90.35	$90.30
Purchase #2	$162.41	7.641%	$174.8197	$174.82	$174.80	$174.80
Purchase #3	$200.67	12.278%	$225.3083	$225.31	$225.30	$225.30
Purchase #4	$164.85	11.745%	$184.2116	$184.21	$184.20	$184.20
Purchase #5	$143.29	10.262%	$157.9944	$157.99	$158.00	$158.00
Purchase #6	$21.57	4.109%	$22.4563	$22.46	$22.45	$22.50
Purchase #7	$108.63	13.767%	$123.5851	$123.59	$123.60	$123.60
7 purchase totals =	$882.33		$978.7074	$978.71	$978.70	$978.70