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	$85.81	4.281%	$89.4835	$89.48	$89.50	$89.50
Purchase #2	$164.51	10.736%	$182.1718	$182.17	$182.15	$182.20
Purchase #3	$209.56	5.238%	$220.5368	$220.54	$220.55	$220.50
Purchase #4	$212.47	7.585%	$228.5858	$228.59	$228.60	$228.60
Purchase #5	$161.35	3.478%	$166.9618	$166.96	$166.95	$167.00
Purchase #6	$200.50	10.236%	$221.0232	$221.02	$221.00	$221.00
Purchase #7	$104.34	12.825%	$117.7216	$117.72	$117.70	$117.70
7 purchase totals =	$1,138.54		$1,226.4845	$1,226.48	$1,226.45	$1,226.50