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	$250.67	13.732%	$285.092	$285.09	$285.10	$285.10
Purchase #2	$111.91	3.474%	$115.7978	$115.80	$115.80	$115.80
Purchase #3	$238.74	7.482%	$256.6025	$256.60	$256.60	$256.60
Purchase #4	$238.62	3.207%	$246.2725	$246.27	$246.25	$246.30
Purchase #5	$72.34	12.164%	$81.1394	$81.14	$81.15	$81.10
Purchase #6	$72.85	13.417%	$82.6243	$82.62	$82.60	$82.60
Purchase #7	$208.37	7.314%	$223.6102	$223.61	$223.60	$223.60
7 purchase totals =	$1,193.50		$1,291.1387	$1,291.13	$1,291.10	$1,291.10